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PVS-7 for prime use: 1.25" or 2" barrel?

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#1 trias702

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Posted 29 May 2020 - 11:41 AM

I'm on the cusp of, I think, maybe finally getting a PVS-7 for NV use with my 85mm refractor.

 

To this end, I'm starting to buy in the accessories I would need to use it in prime focal mode, where I remove the existing objective lens housing, screw in the C-mount adapter, and then attach either a 1.25" or 2" nosepiece for use straight through in my star diagonal.

 

Question is, should I be viewing in prime mode with a 1.25" nose/barrel or a 2"? My star diagonal is 2", but I also have the 1.25" adapter for it.

 

Normally I would go with 2" and not think twice, except for the fact that I know that NV requires all manner of very expensive H-alpha filters to get the most out of it, such as the Chroma line of filters (3nm or 7nm). However, these filters are really expensive, and the 2" filters are nearly double the cost of the 1.25" filters. So given the cost of the filters, I would rather go with 1.25" just to save some money, but are there substantial advantages for 2" when using the PVS-7? Does the PVS-7 have enough aperature in the tube to even fully utilise the full 2" barrel?

 

I suppose going with 2" filters would also allow me to someday use a 2" Ethos eyepiece (with the filter), and attach the PVS-7 afocal to that eyepiece, for crazy wide-field views?



#2 Mazerski

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Posted 29 May 2020 - 11:49 AM

I use 1.25" filters but also have the c-mount to 2" ScopeStuff adapter to use focal reducer. I also have the c-mount to 1.25" adapter as I use devices in this mode too.

 

Will you use in hand-held mode with CCD finder and / or Nikon Lens? The (in my case) 50mm CCD finder with helical focuser amounts to ~ 7x. The CCD Finder is 1.25” focuser opening. 

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Edited by Mazerski, 29 May 2020 - 11:55 AM.


#3 trias702

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Posted 29 May 2020 - 12:25 PM

I use 1.25" filters but also have the c-mount to 2" ScopeStuff adapter to use focal reducer. I also have the c-mount to 1.25" adapter as I use devices in this mode too.

 

Will you use in hand-held mode with CCD finder and / or Nikon Lens? The (in my case) 50mm CCD finder with helical focuser amounts to ~ 7x. The CCD Finder is 1.25” focuser opening. 

I might pick up a finder scope later on, yeah, also with a helical focuser. Are most small (50mm) finders for 1.25" eyepieces rather than 2"?

 

Not sure yet about using a Nikon/Canon lens. If you do use a Nikon lens, how can you also attach a filter, either in 1.25" or 2"?


Edited by trias702, 29 May 2020 - 12:25 PM.


#4 Mazerski

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Posted 29 May 2020 - 12:39 PM

That I have seen, finders are 1.25". What's great about hand-held is that many emission nebulas are huge (I had no idea) and won't fit in FOV of many scopes... to look at the North American at 5 to 7x, looks great.

 

The bottom 2 adapters have a empty filter cell (from cheap color filter) super-glued in and filter screws into blank cell OR, (top adapters) I used nylon rope to hold filter in with blue tape - they easily pop in / out if needed. In the case of Nikon, the adapter is a c-mount to Nikon F body type. Bottom photo left side you see the F -- > C marking. Other users may have come up with different methods in using filters with adapters.

 

As for the focal reducers (if you need)… ScopeStuff sells the 2 inch Antares 0.7x and 0.5x. I use both in the 8 inch Meade LX200 f/10 and a 12.5 New Moon f/4.5. Both FRs focus in both scopes.

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Edited by Mazerski, 29 May 2020 - 12:44 PM.


#5 Eddgie

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Posted 29 May 2020 - 01:09 PM

If you think you will be using a .5x reducer, then vignetting is an important consideration.

 

If you use a 1.25" nose, these usually have about 30mm of length and with the 18mm from the flange to the photocathode distance, and then another 7mm for the filter cell.  you are looking at about 55mm of light path.  At f/3.5, your fully illuminated field will fall from about 26mm to about 10mm in size. Now that is not terrible, but you will see the vignetting at f/3.5,

 

Better would be a short 1.25" nose. This would give you a fully illuminated field of about 14mm and the vignetting would be much milder.  It is a little thing and maybe not a terribly important thing to you but for nebula work, I recommend to people to always try to get the largest fully illuminated field one can.

 

On the left, 15mm of light path.  On the right, 30mm.  Now I used 7nm for the filter cell but many new cells are much longer than this but few are shorter than about this amount. 

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Edited by Eddgie, 29 May 2020 - 01:10 PM.


#6 trias702

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Posted 29 May 2020 - 02:32 PM

If you think you will be using a .5x reducer, then vignetting is an important consideration.

 

If you use a 1.25" nose, these usually have about 30mm of length and with the 18mm from the flange to the photocathode distance, and then another 7mm for the filter cell.  you are looking at about 55mm of light path.  At f/3.5, your fully illuminated field will fall from about 26mm to about 10mm in size. Now that is not terrible, but you will see the vignetting at f/3.5,

 

Better would be a short 1.25" nose. This would give you a fully illuminated field of about 14mm and the vignetting would be much milder.  It is a little thing and maybe not a terribly important thing to you but for nebula work, I recommend to people to always try to get the largest fully illuminated field one can.

 

On the left, 15mm of light path.  On the right, 30mm.  Now I used 7nm for the filter cell but many new cells are much longer than this but few are shorter than about this amount. 

Thank you for the detailed reply, but I'm afraid I'm a little bit confused by some of the numbers, such as that f/3.5. The scope I plan to use is an F/5.3, 450mm, and no plans to use a focal reducer (at least not initially).

 

I understand that a shorter noisepiece is preferable, but otherwise am a bit lost on how to calculate for vignetting on a 1.25" vs 2" nose and how those calcs apply to my specific scope params.

 

So for my use case, with a star diagonal, will I see vignetting at 1.25" with either length nosepiece (15mm vs 30mm)? My scope has 200mm of backfocus (not focuser travel) if that helps.



#7 Mazerski

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Posted 29 May 2020 - 03:58 PM

For the 8” Meade SCT I use a 2” diagonal with its 1.25” adapter and if there is vignetting either I don’t see it or doesn’t bother me. If I use a Focal Reducer, then I use all 2” (with 1.25” filter inside the 2” ScopeStuff adapter). 
 

For 12.5” NewMoon, use 2” ScopeStuff adapter.

 

I also use a 5 slot filter wheel — 2” section slides into 2” focuser and use 1.25” adapter on NV device to slide into wheel. 

 

Focal reducers are very useful in my opinion and I use in both scopes - depends on what I’m looking at.
 



#8 Eddgie

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Posted 29 May 2020 - 05:30 PM

Apologies.. Must have gotten your post confused with another one where someone was going to be using a 130mm f/7 Apo.



#9 a__l

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Posted 29 May 2020 - 06:07 PM

I suppose going with 2" filters would also allow me to someday use a 2" Ethos eyepiece (with the filter), and attach the PVS-7 afocal to that eyepiece, for crazy wide-field views?

You will not get the benefits of ethos.



#10 Mazerski

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Posted 29 May 2020 - 07:07 PM

Trias 

 

Read your initial post again... if you buy a stock off the shelf PVS7, the objective lens and stepped nosepiece is one piece that is not separable. You need to remove the entire piece and replace with a C-Mount nosepiece.

 

https://www.ebay.com...dapter&_sacat=0

 

Photo of my 7 unit above has the stepped nosepiece that is shown in 2nd ebay listing.



#11 trias702

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Posted 29 May 2020 - 07:15 PM

Trias 

 

Read your initial post again... if you buy a stock off the shelf PVS7, the objective lens and stepped nosepiece is one piece that is not separable. You need to remove the entire piece and replace with a C-Mount nosepiece.

 

https://www.ebay.com...dapter&_sacat=0

 

Photo of my 7 unit above has the stepped nosepiece that is shown in 2nd ebay listing.

 

Yes I know this.

 

But once you have that C-Mount nosepiece installed, you then screw on either the 1.25" or 2" barrel adapter from ScopeStuff (like this one: http://www.scopestuff.com/ss_c2bf.htm), which allows you to then stick your PVS-7 with either 1.25" or 2" barrel into a 1.25" or 2" star diagonal, with optional 1.25" or 2" filter threaded on.

 

The question I'm trying to answer with this thread is, should I use the 1.25" barrel adapter (from ScopeStuff or BlueFireball) or the 2"?

 

I ask because the Chroma filters are way cheaper for 1.25", but if I will get vignetting with 1.25" and my telescope specs, then I will just suffer the higher cost of the 2" system and go 2" for everything.



#12 Mazerski

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Posted 29 May 2020 - 09:39 PM

I don’t have a refractor.

A couple CN guys that have Refractors and use NV are Gavster and BobHen, you should ask them your filter questions.

 

Adapters - you will end up (no doubt like the rest of us) using the NV device in different configurations you aren’t thinking about now (What if you buy a 2nd scope, filter wheel...) — play safe and get 1 each 1.25” and 2” ScopeStuff- that’s what I did and use both all the time. 

2” = #C2BF  === $44

1.25” = #C2B1 == $24

 

I Picked up 2 each since I have a Mod3 and PVS7



#13 Eddgie

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Posted 30 May 2020 - 09:18 AM

As I said, you can just use a 1.25" nose. If the scope is f/5 or so, the long one is fine.  Faster than f/5, I would recommend the shorter 1.25" nose.

Unless you are doing afocal with 2" lenses there really is not much need for a 2".  I have scopes as fast as f/2.8 and I only use 1.25" filters. 

 

Also, if you have the NAIT C mount adapter, this will mount in a 2" diagonal and the short nose will prevent the filter from hitting the mirror.  Here is a PVS-7 with the NAIT adapter (and others might work this way as well but I know the NAIT one does) mounted in a 2" focuser.  Mounts the same way in 2" diagonal, but measure to make sure the filter does not hit the mirror, though I never had any problem with this using the short nose in the picture in my earlier post. 

 

PVS 7 in dob.jpg

 

PVS-7.jpg

 

Now if you have some other need for the 2" filter than the Scopestuff adapter might be the better way to go, but I used the C mount with the 1.25" nose and 1.25" in scopes as fast as f/2.8 and it worked well but again, I recommend the short nose for faster scopes or if using focal reducers. 


Edited by Eddgie, 30 May 2020 - 09:21 AM.


#14 trias702

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Posted 31 May 2020 - 12:22 PM

Thank you for that diagram, it is very helpful.

 

Unfortunately, the NAIT C mount adapter is no longer made, I cannot find it for sale new anywhere. But I am hoping the only other one I can find will work too. Although the 2" step on the NAIT seems a bit useless to me because you would still need to attach a 2" nose so you can thread on a 2" filter. I'm assuming you can't put a 2" filter directly on the NAIT 2" step, and without a filter of any kind, a NV system is rather useless no? (or so I've read)

 

Quick question: in your diagram you have the "short 1.25 nose" -- where can I buy this short 1.25 nose? The only 1.25 noses I have seen for sale are the ones by ScopeStuff, BlueFireball, and Baader makes one too. Not sure which of these 3 counts as short.



#15 Eddgie

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Posted 31 May 2020 - 12:46 PM

The short noses are available on eBay from China. Maybe other sources as well.

 

You asked about 2" vs 1.25" filter and the point was that if you went with the short nose, you don't need a 2" filter.  If you want to use 2" filter, then you can use the Scopestuff or you can use a 2" to 1.25" adapter with M48 thread on the end, but this might make it difficult to reach focus in a dob.

 

You would have to call NAIT directly.   The last time I was down there, they had a box of these.  Now maybe they are all gone, but it was a lot of C mounts and there is not all that much demand for them 



#16 jdbastro

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Posted 31 May 2020 - 11:33 PM

Thank you for that diagram, it is very helpful.

 

Unfortunately, the NAIT C mount adapter is no longer made, I cannot find it for sale new anywhere. But I am hoping the only other one I can find will work too. Although the 2" step on the NAIT seems a bit useless to me because you would still need to attach a 2" nose so you can thread on a 2" filter. I'm assuming you can't put a 2" filter directly on the NAIT 2" step, and without a filter of any kind, a NV system is rather useless no? (or so I've read)

 

Quick question: in your diagram you have the "short 1.25 nose" -- where can I buy this short 1.25 nose? The only 1.25 noses I have seen for sale are the ones by ScopeStuff, BlueFireball, and Baader makes one too. Not sure which of these 3 counts as short.

Baader's is pretty short at 18mm insertion length.

 

https://agenaastro.c...ce-2958515.html




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