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Question about the FL80s and cameras

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#1 xandos

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Posted 21 July 2021 - 11:00 PM

Hi all!

 

I've been lurking on these forums for a while, but this is my first post. The occasion is that I've managed to get my hands on a Vixen FL80s (which is why I am posting in the 'classics' section).

 

I am planning to attempt doing astrophotography with it. I'm hoping to get my hands on the reducer at some point, but know that it might be a while before one pops up. In the meantime, does anyone happen to know what parts I need to connect the telescope to my camera? The camera is a full-frame pentax DSLR.

 

Thanks for all the help in advance!


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#2 photoracer18

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Posted 22 July 2021 - 11:58 AM

Depends on the era yours came from and what focuser it has on it. If you are using a K-1 or K-1ii and your focuser is only available with 1.25" you will get some vignetting in the corners regardless if your camera adapter is using a 42mm T-ring or a 48mm T2 ring. Early ones from the 80's like I had had a 2" adapter that was basically unobtainable as no one had made it in decades. So I did research and found an adapter that allowed me to put a Starlight FT2025 2" focuser on it. At that point you would need to use a generic focal reducer like the Tele Vue 2008. There were 2 different focal reducers from Vixen, an FL-80S dedicated one and one that was for both the FL-80/FL-70. Never owned one, just saw them for sale at different times. If you have a 2" version Vixen focuser or the one with the 53mm barrel that does have a current 2" adapter then it depends on whether your images are going to be from a modded or unmodded camera version. I say that because you might want to use filters. Otherwise just buy a 2" to T adapter that accepts 48mm T2 rings and buy the Pentax K 48mm T-ring adapter. Remember to go into the menu and set the aperture control to manual


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#3 xandos

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Posted 23 July 2021 - 12:36 AM

Thanks a lot for all the information. I'm not sure what era mine is from, it is still on the way. The auction pictures of the lens cell were not too great, so I'm hope its in as good a shape as advertised. It looks like this (picture from the auction) and seems to indeed only come with the 1.25" back. I'd assume though, that like earlier versions the 1.25" holder does screw out. and then I should be left with a threaded tube. I'll have to confirm this all when it arrives of course.

 

Vixen still makes these:

https://global.vixen...roduct/3878_09/

 

If I understood correctly, that might fit the FL80s when removing the 1.25" adapter, but I'm not sure, do you happen to know?

 

A pentax-T ring is on the way.

 

So far I've been doing some beginner-level astrophotography with the pentax K-1 (unmodded) and the 300mm prime lens. This will be my first real scope, so I'll have a lot to learn!

 

i-img1200x900-1626651336hgc0ro295922.jpg


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#4 xandos

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Posted 23 July 2021 - 02:35 AM

To anyone else who might be interested, I asked a telescope shop in Tokyo about the compatibility of the new reducers/flatteners for the SD81 etc. to the FL series. It would need to be one of the 60mm drawtube versions to be compatible, so quite a few of the FL scopes with the smaller drawtubes are not compatible.

 

Apparently the performance of these on the FL series is something that vixen has made public, although I had not found the information before. The figures are here:

 

https://www.vixen.co...df/sdhd_old.pdf

 

I'm new to these type of graphs, but if I understand correctly, the flattener and reducer both pretty drastically improve performance.


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#5 xandos

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Posted 26 July 2021 - 06:14 AM

A related question that photoracer18 could perhaps answer:

 

There are a few focusers available that happen to have an M90 thread, that should fit with the telescope. An example is given in this blog in Japanese:

https://nekomeshi312...es/6096428.html

The focuser there was a Kasai trading product, which I think is no longer being sold. However, it seems that TS still has a similar focuser, and also a 2.5" focuser with 90mm female thread:

https://www.teleskop...avel-95-mm.html

 

Would things like this be suitable for the FL80s? Are there issues with not being able to reach focus if the focuser is longer than the original?



#6 RichA

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Posted 27 July 2021 - 02:01 AM

Thanks a lot for all the information. I'm not sure what era mine is from, it is still on the way. The auction pictures of the lens cell were not too great, so I'm hope its in as good a shape as advertised. It looks like this (picture from the auction) and seems to indeed only come with the 1.25" back. I'd assume though, that like earlier versions the 1.25" holder does screw out. and then I should be left with a threaded tube. I'll have to confirm this all when it arrives of course.

 

Vixen still makes these:

https://global.vixen...roduct/3878_09/

 

If I understood correctly, that might fit the FL80s when removing the 1.25" adapter, but I'm not sure, do you happen to know?

 

A pentax-T ring is on the way.

 

So far I've been doing some beginner-level astrophotography with the pentax K-1 (unmodded) and the 300mm prime lens. This will be my first real scope, so I'll have a lot to learn!

 

i-img1200x900-1626651336hgc0ro295922.jpg

The Feathertouch focuser mentioned costs over $500 so you may or may not want to spend that much.  Your scope is right in the middle focal-length wise of what is recommended for generic compress/field flattener lenses.  Astro-Physics makes one for f6 scopes and one for f9 scopes.  Orion makes one for f6 scopes, TeleVue does, as do others.  Most are 2 inch slide-in units that require a 2 inch drawtube.  However, I do not know if you have enough focus in-travel to replace the 1-1/4" draw-tube aperture you have with a 2 inch one.  It may work photographically, with a camera, straight-through, but it may not work visually with a 2 inch diagonal.  You might want to do some measurements.  Scopestuff.com also has a lot of adapters which may help.


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#7 xandos

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Posted 29 July 2021 - 12:27 AM

Thanks!

 

I'll indeed attempt to avoid the feathertouch focuser, because one of the reasons I got this scope was to stay within a small budget.

 

The amount of travel/focus is something I'm also about, how do I determine how much I have to work with and how much I need?

 

I've searched everywhere, but it seems 53mm to anything adapters do not exist. I can have one custom-made (but its pricey) or use one of the intermediate diameters I have with this focuser, which are also non-standard (the threads available are 53mm, 43mm, 36.4mm and 31.7mm).



#8 RichA

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Posted 29 July 2021 - 01:00 AM

Thanks!

 

I'll indeed attempt to avoid the feathertouch focuser, because one of the reasons I got this scope was to stay within a small budget.

 

The amount of travel/focus is something I'm also about, how do I determine how much I have to work with and how much I need?

 

I've searched everywhere, but it seems 53mm to anything adapters do not exist. I can have one custom-made (but its pricey) or use one of the intermediate diameters I have with this focuser, which are also non-standard (the threads available are 53mm, 43mm, 36.4mm and 31.7mm).

Hate to say,  the best way to determine in and out is to actually put the thing being used on the scope and try to focus, always at infinity.  Failing that, determine the exact infinity focus point using something like translucent (wax?, something) material taped over the end of the focuser tube.  You can focus on daylight objects (buildings) at infinity and a projection of the subject will appear on the temporary screen.  This is the infinity focus point of the focuser. It's easy to calculate how much in-focus you'll have for a digital camera, you need to accommodate its flange to sensor distance and any depth added by adapters to use it on your scope.  However, how it will behave with a reducer/corrector is a question, it depends on the specific unit.

 

For some more info check out these:

 

http://www.scopeview.../VixenFL80S.htm

 

http://scopestuff.com/ss_5448.htm



#9 photoracer18

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Posted 29 July 2021 - 05:08 PM

A related question that photoracer18 could perhaps answer:

 

There are a few focusers available that happen to have an M90 thread, that should fit with the telescope. An example is given in this blog in Japanese:

https://nekomeshi312...es/6096428.html

The focuser there was a Kasai trading product, which I think is no longer being sold. However, it seems that TS still has a similar focuser, and also a 2.5" focuser with 90mm female thread:

https://www.teleskop...avel-95-mm.html

 

Would things like this be suitable for the FL80s? Are there issues with not being able to reach focus if the focuser is longer than the original?

The FL-80S needs a focuser with 2.5" of travel and a 90x1mm fixed thread, no threaded collar like an RC one. 2" of travel will work but adding a 1" extension tube to the parts is good for those cases where 2" is a little too short. Its a female 90mm thread also as it goes over the tube.



#10 photoracer18

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Posted 04 August 2021 - 10:59 AM

The TS flattener the TSRED279 is designed for a scope in the F7.8 range, in fact a doublet. That one can be either mounted in a 2" drawtube or can be screwed into a focuser that has a 63mm thread under the top cap, Feathertouch, Stellarvue, and WO 2.5" focuser have this but those are not cheap. Also you can get an adapter to mount it on a 68mm threaded focuser such as used by Zeiss, APM, and Moonlite 2.5" ones.

I have an SVX127D on order from Stellarvue which will get here next month I think. Due to the focuser shortage from Feathertouch (founder passed away and the manager left) I could no longer get it with the FT 3". SV restarted their own 3" focuser production line to fill the gap and reduced the scope price accordingly. However while the SV focuser is a very close match to the FT I already had a 2.5" FT sitting in a box so they agreed to put that on my scope since they already made an adapter to fit between the tube size difference (and reduce the price). So now I will have a 63mm top, and I will be using the TS one which is a close match F-ratio wise and also made for a doublet. The difference between a 3" and a 2.5" focuser, except payload, is non-existent with a scope F-ratio of F8.

 

Hate to say,  the best way to determine in and out is to actually put the thing being used on the scope and try to focus, always at infinity.  Failing that, determine the exact infinity focus point using something like translucent (wax?, something) material taped over the end of the focuser tube.  You can focus on daylight objects (buildings) at infinity and a projection of the subject will appear on the temporary screen.  This is the infinity focus point of the focuser. It's easy to calculate how much in-focus you'll have for a digital camera, you need to accommodate its flange to sensor distance and any depth added by adapters to use it on your scope.  However, how it will behave with a reducer/corrector is a question, it depends on the specific unit.

 

For some more info check out these:

 

http://www.scopeview.../VixenFL80S.htm

 

http://scopestuff.com/ss_5448.htm

Reviewer is wrong about one thing, Vixen fluorite scopes were serialized in the older green mount days, just not in the current white mount phase.


Edited by photoracer18, 04 August 2021 - 11:02 AM.



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