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Nikon FSA-L2 as image erector for astro-telescopes (1 Viewer)

not a 100º but a 82º zoom

Well I didn't tested it with an Ethos because I had a bad experience with the reduced eye-relief of the Panoptic 24mm, that is supposed to have the same eye-relief of the Ethos. So after a not so good test it with the TV Nagler 17mm type 4 (not enough eye-relief and blackouts on daylight use), I tested in with the 22mm Nagler type 4 - bigger eye-relief and no blackouts. With this ep it works well and is parfocal - it results in a 23-81x zoom with a constant 82º AFOV! The 30-104x zoom range of the 17mm would be better for my cr-birding. Will try the BS 1.6x barlow it the 22mm and see if the image quality still is good and it doesn't vignette. The zoom range will be 37-129x so close to the zoom range of the combo with the binoviewer! If it will work, will be nice to compare 82º with one eye vs. the 60º in binomode... :-O
 
The link of the barlow is http://www.bs-astro.com/en/store/accessories/optic-accessories/bs-astro/modular-barlow-125q
It's listed as out of stock but if you are interested send an e-mail since frequently the web-page is not updated.

The barlow works well with the Nagler 22mm and remains parfocal if the barlow is used before the erector. Will have to determine the increase factor to see if it results on 1.6x or not. In a short test yesterday if looked around that magnification and image quality remains good :king:
 
Did a few more tests, used the combo several hours and can add a bit more info.
Adjusting the distance of the barlow to the erector I can eliminate vignetting at lower mag position but image quality suffers. So I prefer to loose a bit of AFOV (5-10º) at minimum power and benefit image quality at higher powers.
Even so at maximum magnification the field isn't completely flat - without the barlow looks much better! probably will find a 2" 1.6x barlow to see if it works better.
Using the BS barlow close to the erector result on about 1.5x increase factor. Will have to do a resolution test.

mono 82º vs. bino 60º
Much prefer the binoview in terms of comfort and definition. The difference in AFOV seems reduced due to bino mode. The mono bigger advantage is the parfocal zoom - better efficiency when searching and reading codes on cr-birding. Light and contrast are also better in mono but only noticeable when passing immediately from mono to bino - seeing with the 2 eyes compensates the decrease in light since the brain uses double info! Will write a test text when having time...;)
 
Maximum TFOV and Ethos experience

I had a chance to try a Celestron Axion 31mm 82º and an Explore Scientific 30mm 82º that maximize the TFOV with the current set-up and the one I preferred was the Axiom - it had completely flat field as opposite to the ES that showed curved field near the limit. Enclose a photo to show how big it is. This solution has low magnifications that can be interesting for some of you but I prefer higher power.
Found a 2" barlow cell that works well - see info at the end of http://www.pt-ducks.com/cr-telescopes.htm#Nikon_FSA-L2
There is also a photo of the combo with a Ethos 17! The resulting image quality is even better than with the Nagler 22 and was surprised to manage to see about 90º AFOV with eye-glasses! Now I know what is to forgot that we are looking through an eye-piece. It was a test that will become expensive since will have to purchase one...
 

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100º AFOV zoom 30-104x / 41-145x!!!

My Ethos 17mm arrived on Friday but only today I had a first test in field conditions. With the TMB92 and the Nikon erector it results on a zoom 30-104x with very good image quality - isn't perfect since the TMB has a bit of field curvature but with Ethos manage to flattened the field. This allows the use of a 2" barlow cell before the erector that result on higher magnifications - 41-145x!!! This is the solution I prefer since the barlow increases a bit the eye-relief and allows me to almost see all 100º with my glasses (at lower magnifications since the FSA-L2 reduces the ER with power increase with zoom). Surprise to me was the fact the 145x are usable with blue sky! :eek!:
Some remarks:
- the TFOV of the Ethos 17 with this combo is a bit larger then with the Nagler 22 - didn't expected that but even better;
- if the Ethos 17 had a bit more eye-relief it would be even better - read that the Nikon HW has better ER - hope that never will test one of those or might be more expensive than the test of the Ethos 17 was...;) For those that money is no problem go for a HW instead of an Ethos - I'm using the Ethos without the rubber eyeguard.
Only next week I will go to my reference cr-birding area where ducks are much closer that might change my preference about the barlow use. Meanwhile will try to do some resolution tests.
 
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From a post on another forum mentioning that at 145x with the TMB92, the image would be a bit dark, I remembered that the 1rst lens of the FSA-L2 moves with zoom and that might would affect the zoom factor. Today I did a quick test to verify the zoom factor and noticed that it's reduced when using the barlow cell (at maximum zoom position the first lens of the Nikon is closer to the barlow lens, so increase less...), and the resulting magnification should be 41-127x so more according the image quality and brightness I observed before and confirmed today...;)
I should add that with this combo, with the barlow, the resulting TFOV are much wider than the 30-90x zoom of the Optolyth 100...:king:
 
`There is also a photo of the combo with a Ethos 17! The resulting image quality is even better than with the Nagler 22 and was surprised to manage to see about 90º AFOV with eye-glasses! Now I know what is to forgot that we are looking through an eye-piece. It was a test that will become expensive since will have to purchase one...`

pic with ethos plz ......am not jealous at all :)
 
60-80º 7x zoom

Still didn't had time to finish the tests with the Nikon HW12.5 but managed to try a Leica Zoom with my combo. That should result in a 7x zoom with 60-80º AFOV that might be interesting if would allow wider TFOV and/or higher resolution than the use of 100/102º eyepieces. The image quality was good but need to measure the TFOV and resolutions, and don't know when I will have a chance to do it since the Leica zoom isn't mine...
Meanwhile I let a photo of the combo...;)
 

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I don't know the exact numbers but when I used the FSA-L2 with the Tak60 it increased the Taks FL too much for my liking. It turned my 20x EP into about a 30x EP. The short side of the FSA's FL is 500mm if I remember correctly and I think if I had used the FSA with a scope with a FL around 500mm I don't think I would have notice very much change in the mags. I don't know for sure though if this is why I saw the magnification increase.

Other then that I liked the FSA as an image erector but I wanted to keep my lower mags below 20x. Since then I've got a scope with a FL of 600mm so I might buy another FSA and try it out with the scope but the dang thing is so dang expensive.
 
JBT,
I reply in this post since makes more sense as is a FSA-L2 related issue.
As the FSA-L2 is a lens erector you need to be able to put the eyepiece at the correct distance from it. There is a distance where the zoom is parfocal and don't induce change in focal length. If you put the eye-piece closer it will work also as a focal reducer (at minimum magnification), and will not be parfocal when zooming. If the ep will be at greater distance the FSA-L2 will work as a barlow and also will not be parfocal when zooming. The biggest improvement I managed to obtain on the FSA-L2 was when I replaced the Nikon F-mount attachment by a specially made T adapter - see it at http://www.pt-ducks.com/cr-telescopes.htm#Nikon_FSA-L2. I was hoping that some astro-telescope/ep producer would release a 2" version based in the Nikon FSA-L2 system, so easier to use and not so expensive, but no one still did it...

Got curious with your Vixen ED114 + Leitz 30mm 88 degree combo. The resulting image doesn't show much field-curvature?
Did you already tested any TV NP or a Tak FSQ for daylight use? I was thinking of buying a Skywatcher ESPRIT ED100 but there are reports indicating that it looses collimation easily and my telescopes jump too much in my 4x4 car...
 
Thanks for the info on the FSA-L2 David. I might have to buy another one and give it a second try. As of now I'm pretty happy using a insta-switch barlow system from Denk though.

As far as my Vixen ED114 and the Leitz yes there is some curvature but it's not too bad. I'd say about 3/4 of the FOV is in sharp focus at one time. When I first started using this combo I could focus the outer edge and get a nice sharp image across the entire FOV but more and more this doesn't work for me as well as it use too. I still get everything in focus but it's not as clean/clear as it use to be when I do this. I guess my eyes are getting too old. I compared a Pentax XW40 and the Leitz and the Pentax did better when it came to curvature in my Vixen but not by much. I'd really like to test out the Leitz with the 31 Nagler or 30mm explore scientific. I really like using the Leitz during the day. The on axis view are very nice but I wonder if a newer design might be better for me.

I have yet to try out a TV NP or a Tak FSQ but I'd like to. I'm like you and have my scopes bouncing around in a 4x4 a lot of the time so I feel a doublet is my best bet. Even though I sometimes wish i had the color correction of a triplet when I'm videoscoping.
 
Test of 82º, 100º and 102º AFOV zooms

Some days ago I updated the info on the use of the FSA-L2 with the use of the Nikon Hw12.5 and decided to rearrange the information creating a new marker http://www.pt-ducks.com/cr-telescopes.htm#Test of 82º, 100º and 102º AFOV zooms

JBT,
The ES100-25 was released that means you can have a 24-84 100º AFOV zoom with the use of the FSA-L2. However don't know if it will be parfocal since on Cloudy Nights was told to need much infocus. With my TMB92 it would result in a 20-71x 100º zoom that is probably the dream of low-power wide field fanatics...3:)
 
144 and 178x work!...

This afternoon I could use the barlow+spacer+Ethos17 and the barlow+HW12.5 http://www.pt-ducks.com/cr-telescopes.htm#Test of 82º, 100º and 102º AFOV zooms, using a couple of hours of light without rain, after some stormy weather that let me and more 100000 people without electricity and water for more than one day...
The interesting thing is that 144x and 178x work on field conditions...:eek!:
Sure the air was clean and "cold" but light conditions weren't the best since sunset wasn't much later. The HW combo showed much wider AFOV than the 2º difference would suggest and image quality was a bit better. I use the HW without the rubber eyeguard since it doesn't scratch my glasses structure.
One side detail:- the Ethos is more digiscopy friendly with my NEX5 zoom lens - the photo is just to show that I could have some Heron voyeurism at high power...:-O They start soon at our latitudes...;)
Will try to do resolution tests during the next weeks, if the weather will allow - strong wind and rain will be back tomorrow...:C
 

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