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Photography with a Skywatcher Esprit 80ED and without! a field flattener

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16 replies to this topic

#1 Peter Zbib

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Posted 18 August 2017 - 11:43 AM

Deleted !


Edited by Peter Zbib, 18 August 2017 - 11:53 AM.


#2 ImNewHere

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Posted 18 August 2017 - 12:32 PM

I was interested in seeing it.



#3 scopenitout

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Posted 18 August 2017 - 01:31 PM

I can guess.

#4 Peter Zbib

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Posted 18 August 2017 - 05:48 PM

Well....

 

The field flattener (FF) came with the scope. I installed it on my camera and just left it there. It does a great job. Excellent for wide field, nebulae, etc.

 

But the 80ED has a focal length of 400mm. The FF acts as a focal reducer. So with the FF, the focal length is around 320mm (info from a seller, not from SW...)

 

320mm for imaging a target such as M57 is not quite enough.... So I decided to remove the FF.

 

To my (stupid) surprise (hence the original message), there was no way I could have screw the camera on the scope. I had thought of using the tube extender of the FF but it wont do.

 

Some head scratching later, I realized that I could not attain a proper back focus without the help of some much longer tuber extender. Searched and found the 6.5 cm camera adapter on the SW site. (hence the deletion of the original message)

 

Took my equipment to my dealer. Ended up buying an M42 T-ring (the FF uses an M48 T-ring), a base extender and two 40mm tube extender. Not sure I will need the 2 to achieve focus but I dont want to waste a night because of this (my dealer agreed to take it back if I did not need the 2nd one)

 

Conclusion: Some thinking is always required... And when you buy your ED80 Esprit, you're not ready for imaging if you dont want to use the FF. Crucial pieces are missing and not even mentioned in the manual.....

 

Now the big question: Will the image quality be good, at the center at least. Say for M33 ?



#5 ChrisWhite

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Posted 18 August 2017 - 06:05 PM

Peter,

 

I'm a little confused by your post.  The Esprit 80 does not have a reducer. SW does not make one for it.  It is simply a field flattener.  FL is maintained at 400mm and focal ratio at f5.

 

Sky-watcher does make another line of scopes with an 80mm and they make 0.85x reducer for it, but it is not compatible with the Esprit (according to SW).

 

You definitely want to keep the FF on.  I don't think it would be good without it.  I'm also not sure how you would determine backfocus, or even if you would have to.  Maybe the focus tube is long enough?  Probably not, but even if you did get it into focus I doubt it would be pretty.  

 

Hope this helps.   


Edited by ChrisWhite, 18 August 2017 - 06:08 PM.

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#6 Peter Zbib

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Posted 18 August 2017 - 06:24 PM

Well Chris, YOU got me confused.

 

I was told by more than one person that the field flattener does act as a focal reducer. One person (Michael S. on DPReview's AP forum) even gave me the focal length you get when using the FF !

 

To be frank, I have no knowledge of the optics involved :-( 

 

See e.g.: https://www.astronom...ombos_c269.aspx

 

Assuming that the FF also acts as a focal reducer, I intend to remove it only for certain "small" (relative to the focal length of the 80ED) targets. Certainly keep it for most nebulae.

 

P

 

PS: Backfocus is given in the manual. With what I now have, I should be able to adjust focus.


Edited by Peter Zbib, 18 August 2017 - 06:25 PM.


#7 ChrisWhite

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Posted 18 August 2017 - 06:38 PM

Peter,

 

I'm not sure where they are getting that info, but it's just a field flattener for the Esprit.  400mm FL and f5. 

 

The manual does list 160mm as the visual backfocus, so you should be able to get that figured out pretty easily, but there is no reason to not use the field flattener.  It's not giving you a wider field of view....

 

I've spent a lot of time trying to figure out how to get a reducer for this scope. I've explored the Riccardi, but the diameter is too large to fit inside the focuser.  I've spoken several times to Skywatcher USA to figure out if there are any reducers that they have heard of working... and they have told me no but they would love to hear about it if I find one.

 

I just ordered a Stellarvue .8 reducer that was made for the SV70 and hoping that I can get that to work but have not tested it out yet.  (That would give a 320mm FL at f4.

 

Can you link to the discussion that you are referring to at DPR?  Thanks,


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#8 Peter Zbib

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Posted 18 August 2017 - 07:27 PM

Will try to find the discussion. It happened a while ago.

 

Actually, it was the technician at the dealer shop who gave me the idea of removing the FF.... Which made sense given what Michael told me. If I remember well, he had the info from a dealer in Europe ...

 

!

 

Anyway, I am going to try this tomorrow during the day. Setup the two config and take pics. The change in focal length should be noticeable !

 

To be continued !



#9 Peter Zbib

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Posted 18 August 2017 - 09:06 PM

Here it is:

 

https://www.dpreview...s/post/58134499

 

Michael checked twice .... : 'As far as I do know, rechecked it, the flattener for the SW Esprit 80/400 is a 0.79x one, so you should have 316mm.'

 

BTW he's clearly a very nice guy, knowledgeable and takes great pics !

 

Given that SW clearly does not know what it is producing and what it sells, I am going to do the daylight test.

 

Even if my camera is modded, I should be able to detect the FL change !



#10 17.5Dob

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Posted 18 August 2017 - 11:50 PM

Michael is a "standup guy" and one of the best photographers I know of. I'd trust his word until you do your own tests.



#11 ColoradoBound

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Posted 18 August 2017 - 11:57 PM

I have that scope and when I plate solve with the ff in place I get a focal length of about 413mm so I don't think the ff is a reducer or any kind.


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#12 Tim

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Posted 19 August 2017 - 01:00 AM

I have the 80 mm esprit and the 120 mm and the field flattener is just that flattner only and doesn't reduce like many other brands do.

#13 ChrisWhite

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Posted 19 August 2017 - 07:19 AM

Here it is:

 

https://www.dpreview...s/post/58134499

 

Michael checked twice .... : 'As far as I do know, rechecked it, the flattener for the SW Esprit 80/400 is a 0.79x one, so you should have 316mm.'

 

BTW he's clearly a very nice guy, knowledgeable and takes great pics !

 

Given that SW clearly does not know what it is producing and what it sells, I am going to do the daylight test.

 

Even if my camera is modded, I should be able to detect the FL change !

 

Peter,

 

The reducer he is referencing is not the SkyWatcher field flattener.  It's the TS Photoline .79x Reducer, which is basically a clone of the Stellarvue .8x reducer.  

 

I found the same DPR thread where michael is talking about this: https://www.dpreview.../thread/4035060

He actually links specifically to the reducer I am referring to: https://teleskop-aus...ucer-4-lenses-0

 

Additionally, on the same website he is talking about you can find the description of the Esprit to state that it is compatible with the TS 0.79x reducer:  "Reducer: The Esprit80 is compatible with 0,79x TSRed279 up to APS-C format. The reducer needs to be mounted halfway into the focuser tube, we can make the proper adapter." https://teleskop-aus...ESPRIT-Triplet-APO-with-flattener-and-flight#m  Michael also quotes this same passage.

 

So, if you are using the TS or SV reducer, then yes it is reducing your scope.  BUT, if you are using the Skywatcher field flattener which is included with the scope at the time of purchase... it is just a field flattener.  It looks like this:   https://www.firstlig...-esprit-80.html

 

 

On the same topic, I just received an SV reducer that I will be testing with the Esprit 80.  I'm hopeful that it will work as I would love to have a 320mm focal length f4 scope.  We'll see if it corrects the full field accurately.


Edited by ChrisWhite, 19 August 2017 - 07:20 AM.


#14 Peter Zbib

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Posted 19 August 2017 - 08:06 AM

Hi Chris

 

After a little bit of research yesterday, I convinced myself you were right. But then CloudyNights became unreachable until a few moments ago...

 

Going to check anyway.

 

I was misled, and presumably Michael too, about the ED80 terminology. I thought it was associated to the Esprit line of telescope. Well, it is not.

 

SW had a FF+FR for its other 80mm refractor. And it does look different.

 

Well, now I have to go back to the dealer and return all the stuff I bought yesterday :-)

 

-----------

 

When I have time, I am going to start a thread on upgrade paths. I feel painted in a corner....

 

But I will be very interested to read your report on the SV FR !

 

I hope you have better skies than we have here....

 

P



#15 Peter Zbib

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Posted 19 August 2017 - 08:58 AM

I did the test. It does confirm that the field flattener is what it is : a field flattener

 

It is NOT a combo: field flattener / focal reducer (even though I own an Esprit ED80 and "the ED80 FF is also a FR". The missing "Esprit" makes a major difference...)

 

I now have to return all the paraphernalia I bought yesterday (no big deal).

 

Oh well, from beginning to the end, I am the one to "blame" (and certainly Michael S. is NOT to blame !). The technical guy at the dealer's shop should know his stuff a bit better but frankly SW's documentation is very much on the light side

 

So my focal length has always been 400mm and gone are my dreams of increasing it (from 320 to 400). M57 is going to stay as small as it was :-(

 

Thanks a lot Chris !



#16 ChrisWhite

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Posted 19 August 2017 - 11:37 AM

Yeah... I know it's a bummer, but glad you got it sorted out. 

 

It's a wonderful little scope at least.  I'm really impressed by the well corrected full field.  Color correction is very good and it's still relatively fast at f5. 

 

I'ts made me genuinely interested in the larger SW scopes, but they don't compare to the speed of my powernewt... so for now I'll stick with that. 



#17 Peter Zbib

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Posted 19 August 2017 - 02:46 PM

I love it too. I received many compliments on the roundness of my stars in the corners (as if I was responsible of the quality of the optics :-)) 

 

But I would definitely love to have a longer focal length. I am always mentioning M57 but there are so many other (infinitely other....) targets that are out of reach.....

 

I still intend to post a message called "Growing up blues". :-)




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