Nikon lens internal clean

Don't try this at home!

Disclaimer: just because I did it doesn't make it a good idea.  In my case it was a gamble of cost of replacement against the extortionate cost of professional cleaning.  Having done a lot of research I was confident that best case would be that I fixed the problem and saved myself some cash and worse case the lens would be in the same condition as when I started.  This is simply a log of what I did.

The lens

Several years back I bought myself a nice Nikkor 40mm 1:2.8 DX macro lens.  Not exactly top of the range Nikon glass but a a good lens never the less.  It was relatively cheap (for a genuine Nikkor) off Amazon, very quiet and a good around portrait and macro lens.  I know some would disagree but I like it and besides it's not fair to compare such lens to pro-glass costing £1000s.

 The problem

Anyway, all was well until I tried to use it for widefield astrophotography.  I started to notice that when I stacked multiple images (subs) there were dark spots (or streaks depending on the tracking) - a sure sign of dust in the optical train.  First stop was the sensor but that was clean and besides it only seem to affect this one lens.  After some meticulous inspection with a loupe I tracked it down to a 'foreign body' stuck to the rear element - on the inside!

(sorry about the quality of the images, they were done in a hurry whilst trying not to lose any bits).

I know that most photography experts will say that all lenses will eventually get dust in them and that it really doesn't make much difference unless it's at a focal point such as the sensor.  (Some even profess that it's impossible for internal dust to affect the images but that's clearly wrong).  The fact is that internal dust and particles will always create small shadows on the image as they are interrupting the light path.  The impact the shadow is dependent on how close they are to a focal point - far away and the shadow is spread out and feint, close and it is small and pronounced.  The truth is that in normal daylight photography involving single frames you probably won't notice the effect (I certainly didn't) and even if you do you can edit them out easily.

If you are engaged in astrophotography, however, these things tend to show up like sore thumbs in your images.  In daylight the small spec may lose you a few photons out of millions but when you're only getting a few photons in the first place it makes quite an impact.  When you then stack dozens of images the effect gets magnified causing dark spots (or smears if your tracking is out).

The cause

Having taken the lens to bits I can see exactly how such things get into the lens.  The lens effectively consists of a bellows-like assembly with the rear element fixed and the front moving in and out.  This relatively small assembly is contained within the considerably larger lens (fixed) housing.  The upshot is that when the lens telescopes in and out it vacuums up particles into the outer housing.(but not into the lens assembly at this point).  Obviously with any semi-sealed telescopic lens assembly there ultimately has to be a vent for air to get in and out,  In the case of my lens this is a small slot right by the bottom edge of the rear element.  It's therefore only a matter of time before something is sucked out of the housing, into the internal tube and from there onto one of the lenses.

The image above shows the slot where the particle entered.

The fix

The challenge having identified the culprit was to find a way of getting it out.  I watched numerous videos of people doing similar things - mainly aimed at fixing the mounting plate it has to be said - but couldn't find any relating to my specific lens.  On the of the older lenses the rear element unscrewed (which would have been ideal) but in my case it seemed to have been glued in.  The only simple means of access I could see was through the small slot (as shown above),

Although the picture above makes it look like quite a simple task, there's quite a bit of dismantling needed to get to that stage.  On the plus side there wasn't any hidden spring-loaded things to shoot out when that last screw was removed :)  I have to say at this point that I could probably have slid off the outer casing and done a more thorough clean but I didn't want to push my luck.

As can be seen above the lens has a very nice metal (not plastic) bayonet mounting ring.  This needs to be removed to gain access to the side of the rear element.  Before this can be done it has to be detached from the small block of contact pins.  This is extremely important as they are connect to the electronics in the housing by a very small and fragile ribbon cable.  On the bright side in the case of this lens the electrical contact to the metal ring itself is via a small spring-loaded pin underneath and not (as in come cases) a very thin wire.

As can probably be seen above, the connector pin block is held in place primarily by the large black inner ring.  Removing this was straightforward - it's held in place by three very obvious screws.  Once the screws are removed it pops out easily.

The ring also acts as a stop for the aperture adjustment lever which pushes against it meaning that there is a small click when the ring is removed - a bit alarming first time.  This also means that you have to move the lever out of the way to reinsert the ring later.

Having removed the inner ring the next step is to detach the contacts from the metal outer ring.  If you don't do this then you can't remove the ring fully and run a real risk of snapping the connecting cable.

The connector pin strip is held onto the outer metal ring by two obvious by extremely small screws. This is were a very fine magnetic screwdriver comes in handy.  The screws are probably only about 1mm long.  Once the block is detached it can be pushed slightly inwards (I.e. safely clear of the outer ring).  Once this is done it's plain sailing to remove the outer ring.  This is held in place by four relatively large screws.

As can be seen above, the outer ring has a long lever attached,  This is what operates the aperture mechanism.  It is therefore necessary (and obvious) that the ring be lifted off vertically.  Also when re-attaching the ring it is important that the lever is carefully inserted back into the small slot from which it was removed (to be honest it won't fit back otherwise),

The outer ring has three small metal gasket rings underneath it.  These are a bit delicate and it is also a good idea to remember there orientation for when you come to re-assemble things later.

Four of the round holes are where the screws go through.  A fifth round hole fits over an alignment pin.  The large hole is where the electrical contact from the lens body sticks through to make contact with the bayonet ring.

So, at this point I'd gained access to the small slot in the side of the rear lens element.  Now came the challenge of attacking the particle adhered to the lens.  The first weapon of choice was my trusty Giottos rocket blower however it made no impact at all,  I did consider using a small wire to poke at the speck but decided against this in case I scratched the lens coating.  Finally, I opted to use a plastic coated wire tie to poke a lens cloth (a fresh FroKnowsPhoto cloth - sorry Mr Polin) into the slot.

The initial problem was that although the slot was reasonably wide on the outside it seemed to narrow considerably on the inside.  This it turned out was due to the fact that the front element was fully retracted and hence almost touching the rear element.  Once I'd figured this out a quick turn of the focus ring made life much simpler.  The next problem was how to navigate the cloth to the offending particle without scraping across the lens element.  The solution was simple - retract the font element slowly compress the cloth (gently) against the particle then reverse the process.  It worked!  The particle was now safely attached to the cloth and easily withdrawn through the slot.

Putting it back together was amazingly easy - essentially the exact reverse of taking it apart,  I was a bit apprehensive as to whether it would still work but thankfully it's all a good as new.  No more annoying dark spots on images and it still auto-focuses - always a bonus :)

Overall a useful learning experience :-)

FunCube meteor detector

After reading the article in the June and July editions of Sky at Night magazine I've been inspired to build myself a meteor detector.

The basic principle behind detecting meteors is very simple; when they hit the atmosphere they momentarily create an ionised layer that reflects radio waves - all you need to do is pick up this reflection.  In fact, people have been doing this for donkey's years using radios and home-made antennas.  Obviously, it's beyond most normal people's means to be firing radio signals up into space however.  The solution is to listen for existing signals being reflected rather than creating your own.  Ideally it needs to be a strong reliable signal that is not going to be detectable normally unless it is being reflected back of the upper atmosphere.  For those of us in the UK there is a convenient radar near Dijon in France on 143.05MHz.

On the PC side of things it's quite simple; all you need is a copy of the free Spectrum Lab application and the appropriate configuration file.  Helpfully, the S@N magazine supplied one.  This simple (and at the same time very complicated) application listens to a sound source and displays the signal in various highly configurable formats.  It can also be set to look for specific events and log them - E.g. the spike caused by a meteor.

So, now all you have to do is get some sort of signal into the PC in the form of sound.  I did consider using one of my old scanner radios but it proved a problem isolating them from the interference produced by the laptop.  In the end I opted for the FunCube dongle as used in the S@N article.  This is a very easy to use yet powerful software defined radio (SDR) designed for receiving data from the FunCube satellites but equally useful for receiving any radio signal on the PC.

At this stage I haven't got as far a building a proper antenna for it.  In fact I tried it for the first time last night using a short length of copper wire strung from our patio door across to the shed :)  However, it worked amazingly well considering.  I picked up all sorts of SW signals whilst testing it during the day.  I wasn't seriously expecting it to pick up meteors though without a better antenna.

Last night I left it set up and running whilst I was out observing.  As luck would have it I saw a bright meteor streak across the sky so I dashed back in to the house to look at the laptop screen.  There it was!  Only a tiny blip but it had been recorded at 22:58:15.

All I need to do now it work on a decent antenna.

For an idea of what its supposed to look like see the S.P.A.M meteor network site.

SkyWatcher Adventurer pt2

A few nights ago I had another chance to have a quick play with the new StarWatcher Star Adventurer.  Below is a shot of it all set up ready to go with my trusty Nikon D7100 sitting on top.  As you may be able to tell I've opted to attach a Manfrotto ball head using the small DLSR adapter supplied (effectively a tiny dovetail with a tripod screw on top) rather than using the dovetail bar.  Using a decent ball head with quick release and friction control is far more straightforward in my opinion than having to unlock the mount's clutch to point the camera.  Having said that if you haven't got a good quality ball head then mounting the camera directly on the supplied dovetail would probably be a far more stable solution.  The Manfrotto 496RC2 ball head was an excellent investment, not just for astrophotography; you can point the camera quickly and easily in any direction without fear of it flopping down against the tripod (friction control) and once locked off it's rock solid. Oh, and it's got a quick release plate - essential for stripping it all down in a hurry when the rain comes :)

As you can also see in the shot above, I've been using the supplied SkyWatcher wedge (thought I may as well persevere with it seeing as I've paid for it).  To be honest it's not all that bad as cheap wedges go.  It didn't seem to solid when I was adjusting it but to give it its due there was no detectable slack or wobble when it was locked off and in use.  I'm still undecided as to whether or not to keep it or revert to using my Manfrotto 410 geared tripod head.  The huge advantage of a geared head is that you can just plonk the tripod down in any spot and then level and orientate the head very easily afterwards.  Polar aligning is also a doddle with the fine adjustment knobs.  The SkyWatcher wedge on the other hand obviously needs you to get your tripod properly leveled and oriented before you start.  Like most wedges you only have a small amount of leeway to adjust and there's no facility for leveling other than altering the tripod legs.  The wedge is, however, far more lightweight than my geared head and looks pretty cool :)

Above is the image I took of Cygnus and the Milkyway.  Not amazing as it was only a handful of 30s subs (19mins total) and the sky was still fairly light, not to mention misty.  Did actually leave it going for about an hour only to return and find it all fogged up and covered with dew :(  The subs are ISO1600 f/8.  I took a few darks and flats also.  Something went horrendously wrong with the flats.  Apart from an annoying dust spot on the sensor moving position between lights and darks (must remember to disable the cameras sensor clean), DSS overcompensated for the vignetting - turning a minor dark vignette into a major white halo.  On the whole I'm fairly pleased with the shot as apart from the bright stars in Cygnus the rest is totally invisible to the naked eye from my light-polluted back garden.  At some stage I must look into CLS filters - I'm reliable informed that you can get slot-in filter plates that fit over the end of the lens (no one seems to make neat clip-on sensor filters for Nikons).

Before I move on to mention the pretty impressive built-in polar scope, above is a shot of my setup in daylight so that you can see the bits.  Starting at the bottom, you can just about make out the top of my Manfrotto 055XPROB tripod.  This is a very sturdy rock-solid tripod that is still light enough to be easily portable.  The top of the pole as a proper mounting plate - just about visible under the black mounting plate at the bottom of the wedge. This means that the wedge has a nice flat secure surface to sit on.  I've seen pictures of people with the wedge fixed to a cheap pan-and-tilt tripod head but it looks very unstable to me.  Far better if possible to fix the wedge directly to the top of the tripod pole.

Working upwards, the next bit is obviously the wedge.  The two screws on the right rotate the wedge using the usual push-pull method.  This doesn't allow very much adjustment, however.  The large lever sticking out to the left is the clamp for the elevation adjustment.  I did expect it to lock things off fully when tightened up but found that it was still quite easy to alter the elevation - that's not to say that the mount was in anyway loose.  The big knob on the left adjusts the elevation of the mount.  As the load on the wedge is never going to be that much (unlike a full sized scope mount) they've gone for a single screw adjuster rather than a pair of push-pull screws.  This makes life much easier. The rectangular block with the SkyWatcher logo is the saddle upon which the actual mount sits.

Above is a view of the various buttons and connections on the side of the mount.  The 'snap' socket is for connecting a shutter release cable.  From what I can gather this triggers once every 100 seconds.  Seems like a solution waiting for a problem to me.  Like most people I suspect I have an interval timer already and failing that the camera itself has one built in also - both of which are far more flexible.  The small USB socket is essentially an external power socket if you don't want to use batteries.  It also allows the firmware to be upgraded (not that there is much to upgrade I suspect).  It seems to run OK on rechargeable batteries but I'd have preferred to have had a more conventional power lead supplied (E.g. one that would connect to my 12v powertank).  As you can see it also has a standard auto-guider port.  It's only going to be able to make RA adjustments as that's the only axis the mount moves in.  As I've already found out it tracks very nicely for 2min wide field shots so I suspect I won't be needing to attach a guider.

Before I move on, above is the polar scope illuminating device that was supplied.  It pokes in the end of the PS and has pretty much the same effect as traditional approach of shining a red torch at the end.  I have to say that I found this gizmo to be a bit poor and ended up using my torch to better effect.  My main complaint is that the min-max dial does not have an 'off' position.  Turning on/off is achieved by unscrewing the battery cover (at the back) to a point where it is just about to spill the battery on the floor. To be fair, the AstroTrac also has a cheap and nasty PS light but at least that lights the actual reticle directly. A big advantage of a torch is that you don't tend to leave it switched on a a fortnight :)

The polar scope is very impressive considering the price.  I've paid far more for much worse.  As you can see it is built in and comes as standard.  Only slight downside is that it looks out through the mount's saddle so you can't PA with the DSLR attached.  You might be able to with the dovetail bar attached as there is a slot in it  but I suspect that anything attached to the bar would still be in the way.  The scope has the usual clock dials if you're into that sort of thing.  Personally I use one of the many phone apps now - far simpler.  If you are setting the scope using the dials then you need to unlock the clutch to be able to rotate it.

Above is a view through the polar scope.  This was taken in daylight but I found it to be just a readable at night.  As can be seen, it's got a nice clean reticle with fairly recent calibrations.  I much prefer this approach as (assuming you're in the northern hemisphere) all you've got to do is drop Polaris into the appropriate bit of the ring (as indicated on your app) rather than line up star with circles etc.  The year calibrations are in theory useful but with my eyesight I can only just about make out the ring :)

On the other side of the mount is the 'speed' dial which controls the tracking rate.  This is fairly self-explanatory and the standard speeds have pictures on them.  The one with the star on is of most use as this puts the mount into the regular 1X tracking rate.  The numbered speeds are intended for 'timelapse' photography I suspect (mount has a timelapse mode).

And finally, there's the battery compartment. Not the easiest of things to get into but it is what it is (I suspect that a few years down the line this may be held on by tape).  It takes four AA cells.  I've been using NiMH rechargeable cells and found they work well enough - certainly good for several hours of use.  The cover also has a handy guide for the hard of thinking printed on the top (which you can't see in the dark without a torch). As you can see the built-in shutter release makes more sense when the mount is used in timelapse mode.  Quite why you're want one shot every two seconds whilst spinning it at 12x sidereal I'm not sure unless I've missed something.

Anyway, I'm very pleased with my new toy so far.  Looking forward to using it later on in the year when the darker nights return.

SkyWatcher Sky Adventurer

Thought I'd do a quick post about my latest toy, the new Sky Adventurer from SkyWatcher.

For those who don't know what it is, it's a small portable tracking head for DSLRs that fits on top of a standard photographic tripod.  I purchased it as a bundle from First Light Optics whom I can highly recommend but in no way connected with.  Tring Astro will probably do you a very good deal also.  You can however purchase the mount on its own.  Until now I've been using an AstroTrac which are extremely good but I have to say this looks like blowing it out of the water in terms of price.

My current set up

In the bundle is...

Sky Adventurer Wedge

The wedge is quite good for the price. It's obviously not quite in the same league as the sort you'd expect on a scope mount but then again it doesn't cost anywhere near as much and doesn't really have to carry much weight.  I particularly like the fact the a single screw adjusts the elevation rather than the traditional push-pull affair (the lever on the side clamps it all off once aligned).  I was in two minds as to whether to use the wedge or carry on with my geared Manfrotto head (which allows fine adjustment in three axes).  To be honest I'm still in two minds - the geared head is better in all respects but not as compact or lightweight as the wedge.  Must point out at this stage that the picture above is a black wedge but as you can see below mine is in sexy red and black to match the mount :)

DoveTail

The dovetail I have to confess is less useful to me as I don't have a scope that I want to mount on it at present.  The large thing sticking up on the left is the DSLR mount.  This is adjustable in that you can rotate the camera and with the ability to rotate the bar on the mount also you could probably point the DSLR in most directions.  It also allows you to mount a DLSR and a scope (albeit a small one) side by side.  To be honest, if you only want to use a DLSR then a decent ball head is far more flexible and much easier to point at your target.  I did experiment with mounting my ball head onto the dovetail but in the end found the DLSR adapter far more straightforward.

DSLR adapter

The small DSLR adapter is my preferred method of connecting my ball head to the mount.  It is in effect a very small dovetail with a screw thread to fit tripod heads.

Manfrotto ball head fitted to the DSLR adapter

There is also a counterweight bar which I don't yet have.  However, I don't really anticipate fitting anything heavy enough to need it.

The mount

And last but not least the mount (shown above on the wedge).  As c an be seen it's got a built in polar scope which is I have to say very good as polar scopes go.  It comes with a small LED light thing that stuffs in the other end - it just about works but is fairly poor IMO (then again the one on the AstroTrac is).  In my experience it is far simpler to shine a red torch at the end :)

View of the connection to the tripod

The picture above shows how it attaches to a 'standard' tripod.  Mine is a typical Manfrotto tripod so the wedge literally just screws to the top.

This is the point where I run out of material :)

So far I've only been able to get outside with it once and being the height of summer it wasn't all that dark.  Polar alignment was a doddle, unlike with the polar scope on the AstroTrac that is on an extending arm (and falls off) the Adventurer's PS is a proper one that goes through the mount's axis.  There's a big ring under the dovetail plate that acts as a clutch.  Loosening this off allows the plate and hence the polar scope to rotate.  As it was light I decided to just take some random shots at ISO100 with my 40mm lens to see how good the tracking was.  To be honest I wasn't expecting it to match the standard of the AstroTrac but was never the lest amazed.  I managed to get some 2min exposures before the light overwhelmed the images.  Below is an image of 5 such frames stacked.  As can be seen the stars are pretty round still.

Rough stack of 5 2min ISO100 40mm frames with Nikon D7100

Crop of raw 2min sub

On the whole, very please with it so far.  Can't wait to try it out properly.

Belton Families Archaeology Walk

Living where we do we are very fortunate to have access to a great National Trust property - Belton House.  There's always so much to do there from admiring the history to just running wild in the parkland.  It's one of those environments where you can't help but enjoy yourself.  We've been going there as a family for quite a few years now and made lots of good friends along the way.

This weekend the NT archaeologist Rachael Hall has been leading archaeology walks around the parkland.  (some may be aware of her through her Radio and TV appearances last week in connection with the coin hoard found in Derbyshire).  Without wishing to embarrass her, she's really good at communicating her passion for archaeology to kids and adults alike.  We joined her walk yesterday (19/7/14) and although the weather got the better of us all in the end (boy was it humid) we all hid a brilliant time.

Above is Rachael explaining the design of the grand avenue leading up from the mansion house to the Belmont Tower in the distance.  Although it is indeed a fair distance compared to the average back garden these days, back in the 17th century it may have been seen as a bit on the average side.  Hence the trees were arranged to create a perspective which leaves no one uncertain as the the fact that this is all yours and yes it does go on for miles.

Full size versions of some of the pics are on my Flickr site for anyone who is interested by the way.

You see a lot of these at Belton if you take time to stroll out into the parkland.  I love the way they come up to you as if to ask what's going on.  As a side note, the Belton parkland is fenced to keep these guys in situ (rather than munching on the formal gardens for cricket pitch) - don't let the fences deter you from venturing out into the park.  There's a large herd of deer also but they're a bit more illusive.

Above is the view back down the avenue from the top.  Back in the day it would have been a much grander affair.  The trees would of course have been slightly different 300 years ago.  The ground would also have been much more level and most likely mown to form a lawn.  The livestock certainly wouldn't have been allowed to roam along it I suspect.  Apart from creating perspective, the avenue served as the driveway for taking carriages up to the tower at the top.  The ladies would be able to sit in the relative comfort of the tower (with a nice picnic and a roaring fire in the winter) and survey the grounds as the men folk went about their business hunting deer.

This large expanse of grass land at the top of the estate is somewhere that many visitors never venture to.  Indeed, I suspect that many don't even know that it is there or don't know it's significance.  99 years ago this area well out of sight of the lords and ladies of the main house was home to tens of thousands of men.  In effect it was a small town with its own amenities and even a railway line.  This was the home of the Machine Gun Corps whilst being trained up before departing for the trenches of WWI.  The staggering statistics are that the Corps sustained 62,049 casualties and 12,498 were killed.  These weren't your usual cannon fodder they were men chosen for their weapons skills etc.  No wonder it was known as the 'Suicide Club'.

Another interesting fact is that this site was ultimately led to the inclusion of women in the police force.  The presence of such a large group of young mainly single men (with to be honest low expectation of surviving very long) next to the town of Grantham caused certain 'issues' in respect to the young ladies of the town.  Hence the first WPC post was created; Edith Smith had the task of policing the 'interactions' and looking after the interests of the lady folk.  She became the first woman in England with the power of arrest.

Time Team did a program on the MGC at Belton back in 2012 (available on 4OD).

Belton House will also be running a programme of events next year (2015) to mark the 100th anniversary.

On our way back.  The building on the left is one of the old well houses that fed water from the wells down to the house.  Some of this would probably have fed the fountain in the formal garden.  At one point the organ was hydraulic but I think that this was powered by a water wheel if I remember correctly.   We had hoped to investigate a few more sites (there's even a lost roman villa here somewhere) but were finally beaten by the heat.

Most important of all the children all had a brilliant time...

First blog, here goes...

So, I thought that I'd have a go at blogging...

I haven't the faintest what I'm going to blog about yet but how difficult can it be :)

Me?
I'm a software developer by profession, married with a couple of kids.

Hobbies and passions?
Astronomy, Photography, Nature, the National Trust.

In case anyone is interested, I'm on Twitter and Flickr