ST102 to 80ED

[Lee_P]

I’m toying with the idea of upgrading my ST102 to an 80ED at some point in the future. I’ve definitely been bitten by the astro imaging bug! The 80ED seems to be a popular choice, and short tube refractors are ace. Can anyone give details of the difference in quality I could expect? I’m slightly concerned about the drop in aperture (102mm to 80mm). Thoughts?

[ronin]

Visually you may not actually get a great deal of difference.

The ED should deliver sharper images then the 102. The eye actually "sees" more when the contrast is better, which is what I would expect the ED80 to deliver.

So the eye will be effected by the drop of 35% in brightness, but you will gain by the better contrast.

The "problem" being which will have the greater effect.

By the way the ED is still a doublet and some CA will be present, even if minor.

[nicoscy]

Actually it is a 62% difference in surface area of the lens (surface area = radius squared x pi).

I had both scopes. For imaging the ED will definitely be miles apart better, with some residual CA. A lot depends on your post processing capabilities and of course a good APO is preferable to ED doublet.

Given that, keep in mind that the images will indeed be sharper, especially at medium to high magnifications where the achro images begin to break down, but then again you offset this gain with a loss in aperture.

Perhaps if you explain the type of viewing you do it would help a bit. 80mm can be pretty sufficient if your viewing goals settle around solar system targets and bright Messier objects.

Pick your poison as they say...

[Lee_P]

Thanks for the replies. To give more info about the type of observing, although it's fun to plonk an eyepiece in, astrophotography is what really interests me. I'm observing from a city so the light pollution already limits me to brighter objects. nicosy, you say that for imaging the ED will be "miles apart" - could you elaborate..?

I've definitely got a lot to learn about processing, especially as I only started a few months ago! So there's plenty of use left in my ST102, but I think it prudent to start planning an upgrade. For reference, the kind of shots I'm currently taking are here: 

Basic stuff, but first steps tend to be!

[nicoscy]

"Tighter" (pinpoint) stars, much less chromatic aberration and more contrast. Maybe not "miles" apart but the difference will definitely be noticeable.

I am a visual observer but I discuss imaging a lot with friends who are engaged in this and having used telescopes with achromatic doublet lenses, ED doublet lenses, APO doublet and triplet lenses, there is a difference every time you jump a level.

I think you will be better served with the 80mm ED scope for imaging. For visual again be it 80mm or 102mm, they are small aperture instruments (says the man who has on order a 60mm custom refractor from Moonraker..) and although the 102mm will have more reach, the 80mm will provide more aesthetically pleasing images.

You could always get the 80mm for imaging and get a 6" f5 reflector for deeper reach which is really moderately priced. Your mount is capable to handle the weight.

Alternatively to keep costs down, you could always buy pre-owned. I think it is fair to say that all astronomy hobbyists are OCD about taking good care of their equipment.

Awesome shots on Flickr by the way!

[m37]

Main visual difference will be less chromatic aberration. Not zero, but less.

Other important things for imaging that are likely to see a significant improvement in the ED model over the ST range are vastly improved focuser with microfocus control, general better build quality, better orthogonality for the imaging plane/objective, less wobble and movement all round, particularly where components are inserted, rotatable focuser, better tension control and smoothness on the focuser, less backlash also therefore more accurate focusing. 

These are all important parts of astroimaging, not just the optics.

There will probably be a weight difference, and also the ED80 is f7.5 with a matched flattener/reducer down to f6.3 vs the ST102 at f4.9.

[Lee_P]

Thanks for the advice everyone, much appreciated! 

[Lee_P]

Quick question: does the ED80 have a Direct SLR Camera Connection, to easily attach a camera on the end? Or is some extra needed?

[Lee_P]

...other than a T Mount, which I already have. Pics of imaging set-ups seem to include an extension tube, e.g. http://www.harrisontelescopes.co.uk/acatalog/Revelation_80mm_Extension_Tube_2_.html

[Thalestris24]

Quick question: does the ED80 have a Direct SLR Camera Connection, to easily attach a camera on the end? Or is some extra needed?

Hi

This was just discussed on another thread ( http://stargazerslounge.com/topic/222981-1st-attempt-at-dslr-at-prime-focusbut-live-view-blank/#entry2398729 )   - yes you will probably need an extension tube to make up the distance lost by not using the star diagonal. But you will also really need the reducer/flattener to reduce exposure times, in which case you may not then also need an extension tube.

Hth

Louise

[Lee_P]

Brilliant, thanks Louise!

[Lonestar70]

Hi Lee-P,

You will need either a 50mm x 2" extension or the SW field flattener/focal reducer (highly recommended).

The FF/FR  can screw directly on to the focuser draw tube, or it can be fitted with a 2" nosepiece fitting (FLO do one for it) which can then also carry a filter (LP or such like). The FF/FR has an M48 thread for the camera t-ring so you would need one of these as well... the standard t-ring (M42 thread) will not fit.

Hope this helps.

Best regards.

Sandy.

[Lee_P]

Hi Sandy,

So with an ED80 and a Field Flattener / Focal Reducer, I'd also need one of these http://www.firstlightoptics.com/adaptors/flo-m48-to-t2-adapter.html to connect it to my Nikon with standard T mount?

[Lonestar70]

Hi Lee-P,

You would be better to use this camera adaptor: -

http://www.firstlightoptics.com/adaptors/skywatcher-dslr-m48-ring-adapter.html

the Nikon version.

It has a larger internal dia than a standard t-ring so less chance of vignetting... it's cheaper too

The nose adaptor is this one: -

http://www.firstlightoptics.com/adaptors/flo-adapter-for-skywatcher-focal-reducers.html

These are the ones I use with my Nikon.

Best regards.

Sandy.

[Lee_P]

That first link says it's for Canon, not Nikon -- unless I'm missing something?

I'm a bit confused about what the FLO Adapter is for. Just if you want to use filters?

Would this set-up work?

80ED -> Field Flattener / Focal Reducer -> M48 to T2 adapter -> Nikon T mount (that I already have) -> Nikon DLSR body?

Thanks for your help!

[Macavity]

At the back of my mind, I envisage a similar "upgrade". But my ST102 was my first telescope (love)... so I intend to rebuild it, almost in entirety - Monorail focusser, ersatz "carbon fibre" sticky-back on the OTA (lol). To use it as a light-weight, portable, "richest field" scope, maybe more, with appropriate filters...

But frankly, I still doubt fast / budget achromats come particularly close to the (expected) quality of the (more expensive) APOs? My "star test" of the ST102 showed significant "other" abberations... "surface roughness"(?) maybe. I get a reasonable diffraction pattern on one side of focus, but an amorphous "blob" on t'other? (But I do intend to revisit / check this!) 

My affection for my ST102 as a portable scope of significant (4"!) aperture is undiminished. I have a MAK150 for planetary viewing - A "stick and string" GSO 8" / F4 Newt as VIDEO light bucket. So I'm still looking to buy an 80mm ED APO at some stage. It just adds to the possibilities? Classical imaging, maybe? I promise to THEN live frugally for my remaining life! 

[Thalestris24]

That first link says it's for Canon, not Nikon -- unless I'm missing something?

I'm a bit confused about what the FLO Adapter is for. Just if you want to use filters?

Would this set-up work?

80ED -> Field Flattener / Focal Reducer -> M48 to T2 adapter -> Nikon T mount (that I already have) -> Nikon DLSR body?

Thanks for your help!

Hi I think it's better to use the M48 to Nikon adapter as there's less narrowing of the optical train so reducing vignetting. It is also more direct which is always a good thing.

Louise

[Lonestar70]

Hi Lee-P,

If you open the 1st link you can select Canon or Nikon version on the right hand side.

Yes the nosepiece is only needed if you also need to fit a filter.

The M48 to T-ring adaptor would work but the M48 camera adaptor has a larger clear bore (less chance for vignetting).

It's length is also set so that the required backfocus distance for the FF/FR is correct... the M48 - t2 version may not guarantee this... it is quite critical.

Best regards.

Sandy.

[ollypenrice]

Aperture is of little importance in AP since you have time on your side. You collect photons by area and over time, something we cannot do with our eyes. It is nice, at a given focal length, to have more aperture in order to have a faster F ratio but you can work without it.

There is a flattener-reducer for the ED80 which would be a good idea. It is a ridiculously good imaging scope for the price.

Olly

[Lee_P]

Thanks for all the advice. I've ordered the ED80; flattener / reducer; and the recommended camera adapter. You've all saved me from a lot of headaches!

[Lee_P]

In case anyone else is wondering what astrophoto benefits an 80ED brings over an ST102, here are some example shots. Obviously not really fair tests, but maybe useful to give an indication of the difference.

ST102
https://www.flickr.com/photos/lee_pullen/14267645459/in/set-72157645635930781

80ED

ST102

https://www.flickr.com/photos/lee_pullen/14586161125/in/set-72157645635930781

80ED

ST102

https://www.flickr.com/photos/lee_pullen/14764892723/in/set-72157645635930781

80ED

[Lee_P]

Gah, the images didn't all display properly... but you get the idea!