Where to repair telescopes and clean their mirrors

[qinjuehang]

Hi everyone, as some would have noticed, I'm new here

I'm from NUS High School, and we are thinking of doing astrophotography, so we would want a good tracking stand. We actually have some good photography equipment but never had a chance to use it.
I was thinking we could use a Vixen Sphnix and a Vixen VMC200L, with a Orion SkyView Pro 100mm ED EQ Refractor (mount resold I think) as guidescope. (We actually have all that!) This setup requires quite a bit of effort (the sphnix stand is not polar corrected and we don't have a polar correction scope, and the VMC200L sadly has mold on the mirror)

I know the VMC200L is awesome, so anyone knows where to get its mirror (actually, more probably the corrector lens) cleaned out? We indeed have a observatory to do astrophotography, but we are looking for something we could bring out.

Any help is greatly appreciated...thanks in advance

[Meng Lee]

Hi,

The scope you have is VMC not VC. The 100ED is bought only the tube without any mount and it was initially meant to be the guidescope for the observatory showa scope.

Using 100ED to guide the VMC on the original sphinx mount will totally tax the mount out.

To get things started, I would not recommend the VMC scope as the focal length is way too long for orginal sphinx mount to take it. (By the way, I am not the person who recommended VMC for your school But I know who recommended haha.)

You do not need the polar scope for the mount as it is useless at the equator.

Meng Lee

[qinjuehang]

I realized it is VMC, it was a typo. (Actually read the Vixen website wrong and mixed up...but I know its the cheaper one lol). I guess we will just level off the alignment to 0 degrees, since it will be only one or two degrees off. The 100ED is well...someone took it off the observatory two years ago, and we never got round to putting it on, and I figured it might be useful for photography. I never found the rings to attach it back on either, strangely.

I think the scope was bought when I was year 1 or so...and no one took it out for 2 years after the goto function became erratic (I think location is entered wrongly)... I know however the newer firmware supports PEC for sphinx mount, and if we get a focal reducer it might be enough even for a CCD (I think our CCD was for guiding the observatory with the 100ED)...but I'm not too sure. The only reason we would use the Sphinx for photography is for overseas stuff anyway. (which is why I figured polar alignment scope is useful. But then again, I might just look into the hole for the polar scope at polaris and that might be enough, especially since we will probably be going to malaysia or Bintan at most.)

If I were not year 1 at that time I would have recommended the Meade LXD75, but this scope and mount is bought (and spending more on a LXD75 would be rather wasteful). We don't have a lot of cash either, with the frequent lightning strikes that always manages to fry some electronics in the observatory. (we are working on a surge protector, after the aircon and motor controller broke down) So I guess we will have to stick to the mount, and this is the only scope we have that has any chance at astrophotography other than the Celestron C-5, and we obviously can't afford a C-11 (Mr Lim would have made it easier), and the C-5 has a focal length of 1k+ as well anyway. I was originally thinking of asking the school to get a new telescope, but since we won't, we would probably have enough cash for a good focal reducer. Maybe we could make do without a guidescope and just spam ISO if using a DSLR with lower exposure (and stack lots for smoothing out noise).

But then, I still need to find a place/person who can confidently clean the objective lens/mirror/whatever of a VMC200L. There are professional services available in Singapore, are there?

On a side note, is it possible to take good nebula pictures without removing the filter on a DSLR? We can't afford to dedicate a DSLR to astrophotography, and thus would not want it to respond to infra-red light most of the time. (Whichever DSLR we use would probably be either personal or borrowed).

[MooEy]

DO NOT EVER ATTEMPT TO CLEAN THAT MIRROR, seek professional help instead. mirror coatings are very soft and not meant to be dry clean in any way. albert would prolly charge u arm + leg, but it's better than damaging it.

How old is the mirror? how dirty is it? if it's just some dust on it, ignore it and move on. if ur already seeing fungus on it, send it in for servicing.

wan to jump into astrophotography? learn proper drift alignment first. sphinx is a very good mount for short unguided exposure. with enough patience you should be able to get some nebulosity out of orion neb or eta carina. and maybe get some stars out of omega centauri.

dun bother with cheap china mounts like cg5-gt or lxd-75. their periodic error are often 2-3x of vixen mounts and shipping would often make them cost as much as the vixen mounts.

~MooEy~

[Meng Lee]

Hi,

Let me mention some points:

1) You will not see polaris in malaysia or bintan, unless u are on a mountaintop
2) The camera in the observatory is ST6 which is yesteryear technology, please do not use it.
3) Reducer/flattener has to be a dedicated one and positioned at the right distance from the CCD plane otherwise the image is worse than before.
4) VMC does have a dedicated reducer.
5) Yes, don't bother with cheap china mounts.
6) Why the obsession of using SCTs for photography? I think the literature out there may have been misleading.
7) You cannot just pump ISO and take short exposures and stack, I think I mentioned the reason in one of the talks to your club about 2 years ago.
8) It's mold not dust, so cleaning it requires special mild fluid. The only professional service is science centre, but the cost may allow u to buy a new vmc. Personally , I clean my own VC.
9) Yes, you can take good nebula pics without removing the filter. It only takes about 4 to 5 times more effort.

Let me emphasize: modifying the DSLR is not for the infrared !!! The filter itself blocks Ha emission wavelength 656.3nm, that's the wavelength we are after! in fact after modifying the DSLR we must make sure the infrared is properly blocked to prevent red halos!

Meng Lee

[qinjuehang]

I know the DSLR is not for infared, but most CMOS sensors are sensitive to infrared and the filter blocks that...I didn't know we still have to filter our infared after that. We are not obsessed with SCTs, but we obviously won't use a 80mm Orion achromat, and a rather cheap one, for that. (Our only other portable scope aside from Dobs). I did consider M42, but it is...down (well almost). So is M31 and M15 if I'm not mistaken (till morning 4+). So I am quite unsure of what to take, except M11 and maybe M13. And possibly Saturn (with my webcam...do I really HAVE to mod it or can I use eyepiece projection? Its a good webcam in itself.)

I guess we can skip polar alignment in that case (from point 2?)

Also, why can't we pump the ISO? Shorter dynamic range? (I was not as enthu about astronomy 2 years back...so...)

If the Vixen is really way too crazy for that mount, we can use the 100ED i guess. Focal length is not exactly short, but is 900mm. And I think its apo, which should be quite ok for photography. The exposure time would have to be way longer though...considering the light-gathering power is a bit more than a quarter.

The price seems rather steep at Science Center, is there anyone who wouldn't mind cleaning it for a relatively small fee? (Maybe a few hundred...we do have quite limited a budget at this time of the year)

[MooEy]

the 100ed is a gd choice, if u can locate one of those 0.8x reducer/flattener for 800-1000mm fl scopes. some luck is required here to get the reducer to chip distance right.

screw scts for imaging, vignetting, light fall off, field curvature, mirror shift/flop, strange internal reflection, dew up issue, soft images, too long fl, too slow, etc etc etc etc etc. the list goes on and on. a cheap 80mm ed refractor beats it by a huge margin. i suspect even the orion 80st is a better choice.

remember the different wavelengths. visually we can see roughly 400-700nm. the most lens are designed for 480nm to 650nm. ccd can see as much as 300nm to 1000nm, thus a uv/ir cut filter is place infront of the ccd chip to reduce the out of focus bloat cause by the uncorrected wavelengths. unfortunately this means the very interesting h-alpha line of 656nm is being cut off as well.

iso is pretty much stretching of histograms/curves. a ccd/cmos chip have a fixed iso, typically iso 200 or so. no magic exist in iso, it doesn't make the pixels on the ccd any faster or gather more light, nor does it amplify any signal. it just cuts off part of ur histogram.

sorry to inform u that drift alignment is everything when it comes to astrophotography. one of the most impt thing is not to scrimp on setting up time.

if there's fungus on the primary mirror, it could very well mean there's fungus on the klestov corrector assembly as well. too much effort to clean it, and it's too much responsibility to shoulder.

~MooEy~

[Meng Lee]

I do suggest you use your Orion Express on the Sphinx mount and try things out with dslr. Although its not apo, u get very blue bloated stars, but it's much easier to start and dive into photography and u will learn far more than any discussion. You will also get to appreciate why certain factors are so important that astrophotographers will agree on the point "get equipment that works no matter the cost and your images will get there".

Meng Lee

[qinjuehang]

Problem is our 80mm refractor is in bad condition...the coatings are all screwy and the eyepiece screw is missing. It was a scope intended for the juniors, and they don't treat school property kindly...they even managed to screw up a Dob, which the seniors always considered an incredible feat.

I guess the next best is the 100ED used along on the sphnix since its light enough (and is not a SCT lol). Of course, we'll need a dovetail. We actually originally considered trying out in the observatory since it is essentially a hassle-free tracking mount...well almost. When it works and is not damaged by lightning. Of course the focal length is rather crazy for beginners like us, but if it is really too high mag we can use the 100ED.

Maybe after that we will try out nicer stuff in Desaru (as usual Cosmocraft, possibly meeting you there! ). I guess I can photoshop or Gimp (I use Linux a lot) the light pollution out (and we have a broadband filter I think, but I'm not sure) but it can't beat just good seeing I guess. I hope there would be good seeing.

But still, I would want to try to fix the VMC even if we won't use it to take photos since it is a awesome scope (by our standards and budget O.O) in itself. I have no idea whether the mold is on the corrector plate or the mirror, they are right on each other and I didn't really dare breath into the scope.

Alternatively, we should try the Celestron C-5 cuz I think it already has a dovetail and would be easy enough.

Also if the ccd is yesteryear tech, would it be ok to "salvage" it as a guider? Or is it even too bad for that...? Its sensor res is about a quarter of a VGA I think, so I'm not sure. It is cooled though, and has good low noise doesn't it? I'm not sure, I know my cosmology and telescopes ok, but have no experience at astrophotography unless you count a point and shoot photo of the moon through the C-5.

Edit: is the 100 ED a fake apo? Because the site says its a doublet lens...

[MooEy]

prolly can work as guider. hook up the sphinx controller to the pc via ascom. use phd guiding to view thru the camera and guide thru ascom. qns, how are u going to mount the guidescope?

what goto system does the showa mount use? ss2k or some other system? if it's ss2k u might be able to get it working with gpusb.

fixing the vmc? if there's fungus somewhere inside the klestov corrector, ur only hope is sending back to vixen. you can take it apart, but u might never be able to get the right spacing and alignment when u put it back.

~MooEy~