11 replies to this topic

[shams42]

If you have a spare 8x50 straight-through finder scope, you can easily convert it to a 200mm f/4 telescope to use with an image intensifier such as a PVS-7 or NVD Micro. With these scopes, this setup will produce approximately 7x magnification and a 5.5 degree field. If you've done astronomy for a while, you probably have a few of these finders sitting unused in a drawer somewhere.

 

As these are cheap achromats, there is tons of CA. The unfiltered view will show very bloated stars. But, as soon as you install a filter, the view improves dramatically.

 

These scopes are great for hand-holding and sweeping the Milky Way. With an H alpha filter, there is enough magnification for very good views of the North American / Pelican, Lagoon, Swan, etc. This little scope is also great for sweeping up and down the star clouds, dust lanes, and dark nebula of the Milky Way.

 

All you need to do is to follow Michael Fulbright's instructions for modding the finder to accept 1.25" eyepieces. These instructions are available here: http://msfastro.net/...cope/index.html

 

Just replace the guide camera with the intensifier's 1.25" nosepiece and you are good to go.

 

The image-intensified finderscope is a good alternative to camera lenses for low-power observing.

 

 

 

 

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[shams42]

I can't describe how fun this setup is to use for sky sweeping. It's great!

 

The star rendition cleans up nicely with some filtration. The 610nm red filter works great and kills a great deal of the LP while still showing nebulas quite nicely. I was able to just make out the North American nebula with this filter in place. The view was similar to the view through unfiltered binoculars at a mag 7 dark site, only I was standing in my mag 4ish driveway after taking out the trash.  

 

This setup is ideal for observing the large dark nebula. These are objects that I would never dream of trying to observe from my home with a traditional telescope due to the heavy light pollution, but they are quite easy to see in the night vision finder / guider.

 

Of course, with an h alpha filter the nebular views are just awesome. The North American becomes astoundingly obvious, surrounded by a faint curtain of nebula to the north. The Pelican is a piece of cake and shows its characteristic shape. The huge IC 1396 nebula is easily visible. Of course, the bright Messier nebulas in the Saggitarius region show tremendous detail. There are huge faint tendrils of glowing gas winding through the southern Milky Way connecting these objects.

 

For those that don't care to engage in a DIY project to adapt the finderscope to accept 1.25" eyepiece barrels, there are a few commercial offerings worth checking out. For example, Orion sells a 50mm f/3.2 finder / guider for about $100. They also sell a 60mm f/4 finder with a helical focuser for about $220. The helical focuser would be a very nice addition.

 

Baader and Stellarvue also sell dedicated finderscopes that would probably work very well.

 

I highly recommend this setup for night vision users.

[PEterW]

Yep, got me looking interestingly at my Orion auto guide finder... Nice 1.25" port ready to go. Long pass of halpha filter?

Peter

[shams42]

Awesome, please post a report!

610nm, IR pass, 12nm H alpha: all work very well.

Next week I should be able to try it with a 5nm h alpha filter.

[PEterW]

My Dave scope apart from the 3x is my 80mm bigger brother, got the tube cut down to enable focal reduction. Nice big 2" helical focusser. Mine is wrapped in rubber sheet so it doesn't get painfully cold when observing at night. Gives nice zoomed in views of the North America and rosette and still (just about) hand holdable, though I prefer lying on the ground looking straight up.

 

cheers

 

peter

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[Doug Culbertson]

Thanks for the tip! I just picked up a used Orion 50mm f/3.2 guide scope here on the CNC. I look forward to trying this out once it arrives next week, and the skies finally clear out sometime in October.

[Jeff Morgan]

With the advent of DSLR's there is an ocean of unwanted manual focus (dumb?) lenses on eBay.

 

I was looking at the Canon FD lenses and there was many to choose from in the 200mm length. The prices seem comparable to or lower than the typical astronomy alternatives. Focal ratios are also faster, and I would think the corrections are also superior.

Edited by Jeff Morgan, 05 August 2016 - 02:51 PM.

[charotarguy]

I was looking at the Canon FD lenses and there was many to choose from in the 200mm length. The prices seem comparable to or lower than the typical astronomy alternatives. Focal ratios are also faster, and I would think the corrections are also superior.

 

I ordered Canon 200mm FD lenses two times, both mentioned in excellent condition on ebay and both came with the aperture ring not working. Luckily both were from US so I was able to send it back. Not sure about superior corrections but I would definitely look at the Samyang/Rokinon lenses, I've used the 24mmf1.4 and 135mmf2 for imaging with success (unfortunately since they are are Sony E mount, it does not have a c mount adapter for it so couldn't use it for NV), however I would think a canon or nikon mount lens should work great for NV with a proper c mount adapter.

[Vondragonnoggin]

 

I was looking at the Canon FD lenses and there was many to choose from in the 200mm length. The prices seem comparable to or lower than the typical astronomy alternatives. Focal ratios are also faster, and I would think the corrections are also superior.

 

I ordered Canon 200mm FD lenses two times, both mentioned in excellent condition on ebay and both came with the aperture ring not working. Luckily both were from US so I was able to send it back. Not sure about superior corrections but I would definitely look at the Samyang/Rokinon lenses, I've used the 24mmf1.4 and 135mmf2 for imaging with success (unfortunately since they are are Sony E mount, it does not have a c mount adapter for it so couldn't use it for NV), however I would think a canon or nikon mount lens should work great for NV with a proper c mount adapter.

 

Nikon 135mm F/2 lens frequently used by me.

 

The bonus is the 52mm filter threads. Easily adapted with a stepdown ring for 2" Ha filters like the Omega 3nm 2" or Baader 7nm I have. These are excellent low power lenses with a very wide view and good correction.

 

Both Canon and Nikon manual lenses have easy c-mount adapters. When shopping for lenses, I look for the 52mm filter threads because I have longpass and Ha filters in 2" format. For larger lenses, I think I halt after 62mm threads. Stepdown rings still work, but you start cutting off aperture.

 

 My Tamron 300mm F/2.8 is my largest lens with ED elements (this is a 4" objective and yields about 7x), but the guy in Korea I bought it from had modified it with a 2" telescope back with brass compression ring, so it easily accepts 2" nosepiece with filter threads or use of the Scope Stuff 2" nosepiece that has the inset 1.25" threads and 2" threads to use either size filter.

 

The Tamron is really too big for handholding and should be mounted though, but it gives great views and is a great comet hunter (pic is with PVS-7)

 

Edited by Vondragonnoggin, 07 August 2016 - 11:24 PM.

[Vondragonnoggin]

This is the Nikon 135mm F/2 on a Ni-Tec 25mm housing with a 25mm Gen 3 tube (approx 65° AFOV)  and big biocular eyepiece for two-eyed viewing.

 

Edited by Vondragonnoggin, 07 August 2016 - 11:36 PM.

[Eddgie]

What is the OD of the lens cell on this finder?

 

I had thought that I would be limited to using the Mod 3 at 3x, but if the tubes are small enough, it dawns on me that I could use two of these on the binocular.  

 

I only need 63mm of IPD, so if the OD of the cell is less than 62mm, I should be good to go.

[outofsight]

Eddgie, I thought you'd already figured that out, that's the very first thing I thought of, but the very next thing I thought of is what it would be like to hold it?

 

Here are your dimensions, if this is what you're talking about, so you're in luck.

 

Main OTA diameter = 53.4mm (2.10")
Dewshield outside diameter = 57.45mm (2.26")

 

Here's the link.

 

http://agenaastro.co...al-focuser.html

 

If it's not what you're talking about, then I don't know what I'm talking about, a distinct possibility either way. Apologies for any misunderstandings.

 

Here's a similar one, depending on your focusing needs, etc.

 

http://agenaastro.co...uide-scope.html

Edited by outofsight, 18 August 2016 - 02:08 PM.