Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Field flattener for visual?

  • Please log in to reply
90 replies to this topic

#1 davidgmd

davidgmd

    Skylab

  • *****
  • topic starter
  • Posts: 4,083
  • Joined: 24 Dec 2020
  • Loc: Maryland

Posted 11 September 2021 - 11:11 AM

Another novice question:

 

Will a field flattener be of any use for visual observation in a triplet refractor if one is using wide AFOV eyepieces (85o-100o) and is too old to have any accommodation left? Will it make the stars sharper at the edge of the field without having to refocus?

 

Specifically wondering about the AP 92FF field flattener (https://www.astro-physics.com/92ff) for use with the AP Stowaway (https://www.astro-physics.com/92f665) and 85o or wider AFOV eyepieces.


Edited by darkandstormynight, 11 September 2021 - 11:12 AM.

  • thecelloronin and teashea like this

#2 rexowner

rexowner

    Surveyor 1

  • *****
  • Posts: 1,642
  • Joined: 13 Aug 2017
  • Loc: SF Bay Area, CA & Twin Cities, MN

Posted 11 September 2021 - 11:37 AM

AP92ff.png I don't see how you would even do this.  I recently got a Stowaway through the drawing, and

purchased the 92ff, and a Canon camera adapter.  As you can see in the pic, the "eye-side"

(top of 92ff in picture) is threaded to mate withe e.g. the camera adapter.  Really meant for

astrophotography I blv.


  • teashea likes this

#3 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 42,798
  • Joined: 18 Dec 2007
  • Loc: Right Coast of the Chesapeake Bay

Posted 11 September 2021 - 12:04 PM

"Field flattener for visual?"

 

Yes.

 

I am 100% visual.  I use the TSFLAT2 for several of my APO's and achromats.  The result is a flat field from edge to edge.

 

An ST80 with a flat field.  A 6" f/5 achromat with a flat field.  Imagine that ...  waytogo.gif

 

By the way, I am 65 and my eyes have no accommodation for focus.  So if the field looks flat to me, the field is flat.

 

Mike


Edited by Sarkikos, 11 September 2021 - 12:22 PM.

  • CollinofAlabama, Jon Isaacs, vkhastro1 and 8 others like this

#4 rexowner

rexowner

    Surveyor 1

  • *****
  • Posts: 1,642
  • Joined: 13 Aug 2017
  • Loc: SF Bay Area, CA & Twin Cities, MN

Posted 11 September 2021 - 12:34 PM

Last post made me think about this more.

 

If you're really determined to do this, one way would be to get an adapter from precise parts:

https://www.precisep...in/adapter-ctrl

that goes from the 2.74"x24 male threads of the 92ff to the diagonal threads on the Baader

2" diagonal the OP asked about elsewhere - you can remove the nosepiece on the

diagonal  (I don't remember if the Baader side is male or female, and exact threads).

 

This is one way it could work.  I'm not sure about spacing but the Stowaway's focuser

does have about 90mm of travel



#5 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 42,798
  • Joined: 18 Dec 2007
  • Loc: Right Coast of the Chesapeake Bay

Posted 11 September 2021 - 01:17 PM

The TSFLAT2 has standard 2" threads that can screw directly onto the barrel end of a 2" diagonal.  If you have a diagonal with T2 threads when you remove the barrel, you can screw the TSFLAT2 onto the diagonal with a 2" - T2 adapter.  The focal length of the telescope basically determines whether you attach the TSFLAT2 to the barrel of the diagonal or directly to the diagonal.

 

I've used this setup with 100 degree eyepieces.  Doesn't matter.  The field is still flat edge to edge.

 

Mike


Edited by Sarkikos, 11 September 2021 - 01:18 PM.

  • CollinofAlabama, vkhastro1, ewave and 4 others like this

#6 davidgmd

davidgmd

    Skylab

  • *****
  • topic starter
  • Posts: 4,083
  • Joined: 24 Dec 2020
  • Loc: Maryland

Posted 11 September 2021 - 02:54 PM

Thanks all.

 

Mike, I'm the same vintage so it sounds like a field flattener would help me. If I could figure out how to attach it.

 

Sounds like the TSFLAT2 works with a range of scopes from f/4 to f/9. The Stowaway has a 2.5" focuser and comes with a 2" adapter, so I guess the TSFLAT2 will screw right into the AP adapter.

 

EDITED after reading your post more carefully: Sound like a 2" diagonal will attach directly to the "eye side" of the TSFLAT2, or with a readily available 2" to T2 adapter for the Baader T2 diagonals.

 

Rexowner, thank you for taking the time and posting the link. The input data didn't persist when I clicked it. 

 

On the Precise Parts site, I'd pick the AP 92FF for the scope side?

 

For the eye side and the AP MaxBright diagonal, I'd need the "A-P 92 Stowaway f/6.65 DoveLoc adapter?" For a Baader 2" diagonal, the eye side would be the "Baader two inch diagonal body - native?"

 

Looking at the diagram on the AP site at https://astro-physic...aging-train.pdf, I think the train would be:

  • Scope -> AP Focuser end cap -> AP 92FF field flattener -> Precise Parts adapter -> AP 2" Doveloc adapter -> Diagonal -> Eyepiece

 

I should call AP to confirm. Between the $550 field flattener and $150 for the custom adapter, this might remain no more than a thought experiment.

 

Unless I can get the TSFLAT2 to work without additional adapters or spacers...


Edited by darkandstormynight, 11 September 2021 - 02:59 PM.

  • Sarkikos likes this

#7 areyoukiddingme

areyoukiddingme

    Voyager 1

  • *****
  • Posts: 11,271
  • Joined: 18 Nov 2012

Posted 11 September 2021 - 03:10 PM

I have the A-P diagonal, which I use with my Stowaway. 

 

The TS flat will screw directly to the telescope end of the diagonal, but it won't give optimal correction. Though I find it works well with some eyepieces, but not others.

 

My guess is that you would want a diagonal where the TS flat screws directly into the diagonal to replace the nose piece, so not the eyepiece end.

 

I suspect this is what Mike and others have been doing with their short focal length refractors, but it would be good to hear specifically from someone who is getting good correction with their stowaway.

 

I have 4 or 5 diagonals, but the TS flat does not connect directly to any of them, unfortunately. So if you do go that way, finding a model of diagonal that will work is needed, or perhaps an adapter can do the same job.


  • Jon Isaacs, Stellarfire and davidgmd like this

#8 rexowner

rexowner

    Surveyor 1

  • *****
  • Posts: 1,642
  • Joined: 13 Aug 2017
  • Loc: SF Bay Area, CA & Twin Cities, MN

Posted 11 September 2021 - 05:45 PM

Probably depends where it is in the light path, and may not be a major issue, but FWIW,

T2 inner diameter is ~38mm,  which is less than the field stop for longer FL 2" eyepieces.



#9 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 42,798
  • Joined: 18 Dec 2007
  • Loc: Right Coast of the Chesapeake Bay

Posted 11 September 2021 - 05:59 PM

The TSFLAT2 screws onto the telescope-end of the diagonal.  It does not go between the diagonal and the eyepiece.  The TSFLAT2 will insert into the focuser tube.

 

In my experience, the TSFLAT2 works well - optimally or very close to it - with every refractor I've tried it with (look at my sig).  On the other hand, I don't have a Stowaway.  By "optimally or very close to it," I mean sharp stars from edge to edge, even in a 100 degree eyepiece.  (I have not seen vignetting.)  How well it flattens the field depends on if you attach it to the barrel* of the diagonal or directly to the bottom of the diagonal.  I have not seen that the flattening of the field varies in any significant degree depending on the eyepiece.

 

* The barrel of the diagonal is the tube on the diagonal that is inserted into the focuser tube of the refractor.

 

Mike


Edited by Sarkikos, 11 September 2021 - 06:11 PM.

  • vkhastro1, Stellarfire and davidgmd like this

#10 rexowner

rexowner

    Surveyor 1

  • *****
  • Posts: 1,642
  • Joined: 13 Aug 2017
  • Loc: SF Bay Area, CA & Twin Cities, MN

Posted 11 September 2021 - 06:01 PM

Thanks all.

 

Mike, I'm the same vintage so it sounds like a field flattener would help me. If I could figure out how to attach it.

 

Sounds like the TSFLAT2 works with a range of scopes from f/4 to f/9. The Stowaway has a 2.5" focuser and comes with a 2" adapter, so I guess the TSFLAT2 will screw right into the AP adapter.

 

EDITED after reading your post more carefully: Sound like a 2" diagonal will attach directly to the "eye side" of the TSFLAT2, or with a readily available 2" to T2 adapter for the Baader T2 diagonals.

 

Rexowner, thank you for taking the time and posting the link. The input data didn't persist when I clicked it. 

 

On the Precise Parts site, I'd pick the AP 92FF for the scope side?

 

For the eye side and the AP MaxBright diagonal, I'd need the "A-P 92 Stowaway f/6.65 DoveLoc adapter?" For a Baader 2" diagonal, the eye side would be the "Baader two inch diagonal body - native?"

 

Looking at the diagram on the AP site at https://astro-physic...aging-train.pdf, I think the train would be:

  • Scope -> AP Focuser end cap -> AP 92FF field flattener -> Precise Parts adapter -> AP 2" Doveloc adapter -> Diagonal -> Eyepiece

 

I should call AP to confirm. Between the $550 field flattener and $150 for the custom adapter, this might remain no more than a thought experiment.

 

Unless I can get the TSFLAT2 to work without additional adapters or spacers...

 I believe that if you want to essentially replace the nosepiece on a 2" Baader Planetarium diagonal with the flattener

the thread is a 2" SC Thread.  BP is distributed by Alpine Astronomical in Idaho.  They are experts in all things Baader.

 

To make it more complicated, you had mentioned possibly wanting to do NV in the future with the BBHS diagonal.

FWIW, I do NV with Baader BBHS diagonals, and if you do NV, it's handy to swap filters in and out without having

to screw them into each individual eyepiece etc.  E.g., you might want to use a narrowband HA filter for a nebula,

and use a different long pass filter to allow stars to be seen as well.  For that, I use the Baader UFC system, which

I highly recommend, and you could use for NV filters whether or not you use a flattener.

 

FWIW, IIRC my 2" setup is:

Eyepiece Side

Baader 2" BBHS with nosepiece removed p/n 2456115 <--(2" SC thread)-->Baader p/n 2459120 <--(UFC std)-->

Baader p/n 2459110 UFC Base <--(S70 std)--> Baader p/n 2459128 <--(2" SC thread)--> 2" nosepiece from diagonal

Telescope Side

 

-> so, in theory, a precise parts 2" SC thread <--> threads to flattener adapter and use this with a 2" Baader diagonal

with or without the filter drawer.

 

I have a similar T2 setup I can use with 1.25" eyepieces and just about any filter, since the Baader UFC system allows

for different size filters.

 

Personally, I went for a filter drawer which optimized for NV filters, or e.g. density neutral filters for moon viewing etc,

and use flatteners only for astrophotography.  Ease of use of different filters was a bigger deal for me, but YMMV.


  • davidgmd likes this

#11 rexowner

rexowner

    Surveyor 1

  • *****
  • Posts: 1,642
  • Joined: 13 Aug 2017
  • Loc: SF Bay Area, CA & Twin Cities, MN

Posted 11 September 2021 - 06:11 PM

The TSFLAT2 screws onto the telescope-end of the diagonal.  It does not go between the diagonal and the eyepiece.  The TSFLAT2 will insert into the focuser tube.

 

Mike

I'm not personally familiar with the TSFLAT2.  It does look like there are M48, M68 and M69 and maybe more adapters.

 

If a flat field for visual only was the biggest deal for me, personally, I'd get an NP-101 for about the same money

as the Stowaway, and not mess around.  By the time you add the flattener etc, it's probably a more expensive

solution.


  • Sarkikos and davidgmd like this

#12 davidgmd

davidgmd

    Skylab

  • *****
  • topic starter
  • Posts: 4,083
  • Joined: 24 Dec 2020
  • Loc: Maryland

Posted 11 September 2021 - 07:20 PM

I'm not personally familiar with the TSFLAT2.  It does look like there are M48, M68 and M69 and maybe more adapters.

 

If a flat field for visual only was the biggest deal for me, personally, I'd get an NP-101 for about the same money

as the Stowaway, and not mess around.  By the time you add the flattener etc, it's probably a more expensive

solution.

LOL, agreed! My first scope is an NP101, and it is flat, but too big to take on a plane as carry-on. I got lucky and was drawn for the Stowaway, which will be my travel scope for the beach, the 2024 eclipse, etc. I’m still a rookie, thus the basic questions. Appreciate the detailed feedback (post #10)!



#13 davidgmd

davidgmd

    Skylab

  • *****
  • topic starter
  • Posts: 4,083
  • Joined: 24 Dec 2020
  • Loc: Maryland

Posted 11 September 2021 - 07:24 PM

I have the A-P diagonal, which I use with my Stowaway. 

 

The TS flat will screw directly to the telescope end of the diagonal, but it won't give optimal correction. Though I find it works well with some eyepieces, but not others.

 

My guess is that you would want a diagonal where the TS flat screws directly into the diagonal to replace the nose piece, so not the eyepiece end.

 

I suspect this is what Mike and others have been doing with their short focal length refractors, but it would be good to hear specifically from someone who is getting good correction with their stowaway.

 

I have 4 or 5 diagonals, but the TS flat does not connect directly to any of them, unfortunately. So if you do go that way, finding a model of diagonal that will work is needed, or perhaps an adapter can do the same job.

AYKM, can you clarify? Does the TS flat "screw directly to the telescope end of the" AP Maxbright,  or does it "not connect directly?"



#14 davidgmd

davidgmd

    Skylab

  • *****
  • topic starter
  • Posts: 4,083
  • Joined: 24 Dec 2020
  • Loc: Maryland

Posted 11 September 2021 - 07:28 PM

The TSFLAT2 screws onto the telescope-end of the diagonal.  It does not go between the diagonal and the eyepiece.  The TSFLAT2 will insert into the focuser tube.

 

In my experience, the TSFLAT2 works well - optimally or very close to it - with every refractor I've tried it with (look at my sig).  On the other hand, I don't have a Stowaway.  By "optimally or very close to it," I mean sharp stars from edge to edge, even in a 100 degree eyepiece.  (I have not seen vignetting.)  How well it flattens the field depends on if you attach it to the barrel* of the diagonal or directly to the bottom of the diagonal.  I have not seen that the flattening of the field varies in any significant degree depending on the eyepiece.

 

* The barrel of the diagonal is the tube on the diagonal that is inserted into the focuser tube of the refractor.

 

Mike

OK, looks like the TSFLAT2 is the way to go if I’m bothered by field curvature. Thanks Mike!


  • Sarkikos likes this

#15 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 42,798
  • Joined: 18 Dec 2007
  • Loc: Right Coast of the Chesapeake Bay

Posted 11 September 2021 - 07:39 PM

I'm not personally familiar with the TSFLAT2.  It does look like there are M48, M68 and M69 and maybe more adapters.

 

If a flat field for visual only was the biggest deal for me, personally, I'd get an NP-101 for about the same money

as the Stowaway, and not mess around.  By the time you add the flattener etc, it's probably a more expensive

solution.

However ... if you have a number of refractors - AP, ED or achro - that are not Petzvals, the TSFLAT2 can flatten their fields.  So now I have a flat-field 80mm f/5, a flat field 92mm f/5.5, a flat field 102mm f/4.5, a flat field 120mm f/5, a flat field 150mm f/5, etc.  And none of these were flat field telescopes when I bought them.  Cost effective?  Yes!

 

Mike


Edited by Sarkikos, 11 September 2021 - 07:39 PM.

  • Stellarfire and rexowner like this

#16 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 42,798
  • Joined: 18 Dec 2007
  • Loc: Right Coast of the Chesapeake Bay

Posted 11 September 2021 - 07:44 PM

Both ends of the TSFLAT2 are standard 24mm threading.  The end that goes on the diagonal has male threading.  The end that goes into the focuser has female threading, so you can screw a filter onto that end.

 

Mike


  • davidgmd likes this

#17 areyoukiddingme

areyoukiddingme

    Voyager 1

  • *****
  • Posts: 11,271
  • Joined: 18 Nov 2012

Posted 12 September 2021 - 12:40 PM

AYKM, can you clarify? Does the TS flat "screw directly to the telescope end of the" AP Maxbright,  or does it "not connect directly?"

The A-P diagonal body is all one piece of metal, so the 2" tube that connects to the telescope is not removable.

 

The TS flat does screw into that 2" tube. 

 

When I was saying "connect directly", I should have clarified. Many diagonals have a removable 2" tube that goes into the telescope. The TS flat can screw into the diagonal body in place of that 2" tube.

 

Doing so would give you optimal (or close to) spacing to get the right field flattening.

 

I find that screwing the TS flat into the end of the 2" tube on the diagonal helps with some eyepieces better than others.



#18 Mark9473

Mark9473

    Hubble

  • *****
  • Posts: 13,428
  • Joined: 21 Jul 2005
  • Loc: 51°N 4°E

Posted 12 September 2021 - 12:57 PM

Sorry but that's still confusing. Which of the two positions is best?

#19 davidgmd

davidgmd

    Skylab

  • *****
  • topic starter
  • Posts: 4,083
  • Joined: 24 Dec 2020
  • Loc: Maryland

Posted 12 September 2021 - 01:48 PM

Thanks Scott.

 

Mark, I think what’s being said is that the flattener goes between the scope's focuser and the diagonal. And that the flattener works best when the nosepiece of the diagonal (on the scope side) can be removed. The flattener then attaches directly to the scope side of the central body of the diagonal that houses the mirror or prism.

 

When the diagonal's nosepiece can’t be removed (as in the AP MaxBright), the longer optical path reduces the flattener's effectiveness to some degree, more so for some eyepieces than others.

 

Scott, Mike, or Rexowner will correct me if I’ve muddled this up.


  • Mark9473 and areyoukiddingme like this

#20 areyoukiddingme

areyoukiddingme

    Voyager 1

  • *****
  • Posts: 11,271
  • Joined: 18 Nov 2012

Posted 12 September 2021 - 01:57 PM

Yes, that's what I was attempting to say.

 

But . . . the exact light path depends on the focal length of the telescope.

 

Doctordub (Jonathan) put a table into that previous thread here:

 

https://www.cloudyni...l/#entry7708234

 

The take away is that the longer the focal length of the scope, the further out from the diagonal the TS flat should be.

 

With an 80mm F6 (480mm of focal length), attaching the FF to the nose piece of the diagonal is probably pretty close to right.

 

With a 92mm F6.65 (612mm of focal length), then you want to be closer to the diagonal, so replacing the nose piece with the TS flat ought to be closer to optimal for correction.


  • Mark9473 likes this

#21 davidgmd

davidgmd

    Skylab

  • *****
  • topic starter
  • Posts: 4,083
  • Joined: 24 Dec 2020
  • Loc: Maryland

Posted 12 September 2021 - 02:15 PM

So maybe  a Baader ClickLock diagonal and TSFLAT2 would be the way to go. If I could find one, a BBHS mirror could be used for night vision as well:

 

000E8B8E-C66F-43E1-8AF3-70479CD10A00.jpeg

https://www.baader-p...lock-clamp.html

 

This apparently has a T2 thread when the nosepiece is removed? Would a Precise Parts adapter for that be: "TSFLAT2" to "Baader 2 inch diagonal body - native?"


  • teashea likes this

#22 rexowner

rexowner

    Surveyor 1

  • *****
  • Posts: 1,642
  • Joined: 13 Aug 2017
  • Loc: SF Bay Area, CA & Twin Cities, MN

Posted 12 September 2021 - 02:30 PM

So maybe  a Baader ClickLock diagonal and TSFLAT2 would be the way to go. If I could find one, a BBHS mirror could be used for night vision as well:

 

attachicon.gif000E8B8E-C66F-43E1-8AF3-70479CD10A00.jpeg

https://www.baader-p...lock-clamp.html

 

This apparently has a T2 thread when the nosepiece is removed? Would a Precise Parts adapter for that be: "TSFLAT2" to "Baader 2 inch diagonal body - native?"

The 1.25" diagonals have T2 threads -- IIRC correctly male on eyepiece end, female on telescope end,

but double-check.

 

T2 is not large enough for the 2" diagonals and wide eyepieces.  The 2" diagonals have:

S58 dovetail on both ends, each with M55 and 2"-SC-threaded insert ring

 

 

Go to this page, scroll down the downloads section and downoad

the "Instruction Manual".  Good info on the Baader diagonal specs there.

https://www.baader-p...lock-clamp.html


Edited by rexowner, 12 September 2021 - 02:33 PM.


#23 davidgmd

davidgmd

    Skylab

  • *****
  • topic starter
  • Posts: 4,083
  • Joined: 24 Dec 2020
  • Loc: Maryland

Posted 12 September 2021 - 03:07 PM

That Baader instruction manual is great, thanks!

 

I’m still confused about what adapter I’d need to connect the TSFLAT2 to the body of this Baader diagonal with the nosepiece unscrewed: 

https://www.baader-p...lock-clamp.html

 

The TSFLAT2 would go right into the 2" adapter for visual use that comes with the Stowaway (where the 2” diagonal normally goes).

The "scope" side of the Precise Parts adapter would be the Teleskop Service TSFLAT2. It screws on to the "eyepiece" side of the TSFLAT2.

The "eyepiece" side of the Precise Parts adapter, to which the Baader diagonal body (nosepiece removed) would attach, would be:

  1. Baader 2 inch ClickLock adapter S58 (2956258)? Or,
  2. M55? I don’t see that in the PP drop-down for Baader. Or,
  3. Baader 2 inch ClickLock adapter SC/HD (2956220)?

OK, send me off to the corner with the dunce cap…


Edited by darkandstormynight, 12 September 2021 - 03:56 PM.


#24 213Cobra

213Cobra

    Viking 1

  • -----
  • Posts: 849
  • Joined: 24 Aug 2018
  • Loc: Los Angeles, California, USA

Posted 12 September 2021 - 04:12 PM

For visual use, TSFlat2 screws into the diagonal body, or onto the end of the diag nose piece. Or, with smaller-increment spacers, it + the spacers become the nosepiece of the diagonal.

 

If you want to be precise about the working distance, the prescribed distances from TS' website are:

 

The recommended distances from the M48x0.75 thread of the corrector. In principle this rule applies: the shorter the refractor´s focal length, the longer the working distance to the sensor has to be.

 

♦ focal length < 450 mm: 128 mm
♦ focal length 450-490 mm: 123 mm
♦ focal length 500-550 mm: 118 mm
♦ focal length 560-590 mm: 116 mm
♦ focal length 600-690 mm: 113 mm
♦ focal length 700-800 mm: 111 mm
♦ focal length ab 800 mm: 108 mm

 

An underrun or an overrun of the distance of up to 5% has no visible effect on the sharpness in the field of sensors with formats up to APS-C. With larger sensors, the tolerance is reduced to 1-2%.

 

You measure the working distance from the M48 thread on the diagonal side of the TSFlat2 to the field stop of the eyepiece (which is a stand-in for an AP sensor. Knowing the optical distance of your diagonal helps remove guesswork. The reason there is leeway visually is because of the note that "underrun or overrun of the distance up to 5% has no visible effect on sharpness..." That's 10% of distance swing. So for example, on an 80/480 refractor calling for 123mm of working distance, the acceptable range for visual or an APS-C sensor is 116.85 - 129.15mm. This is why either attaching to the nosepiece or the diagonal body tends to be good enough, either/or, depending on scope. But you can put together something more precise with spacers, instead of the standard nosepiece. Of course if you are obsessive about it, then you still have to deal with eyepieces variability in field stop locations. Which is not worth worrying about. I think the distance error tolerance for visual is actually somewhat beyond 5%. I'm 67 and had cataract surgery 17 years ago. My ocular accommodation is gone, other than squinting. With my 80/480 LOMO, screwing the TSFlat onto the nosepiece of an AP Maxbright gave me a visual field as flat as my flat field FSQ-85ED. 

 

Don't sweat it. TSFlat2 works for visual.

 

Phil


  • ad701xx, Jon Isaacs, doctordub and 3 others like this

#25 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 42,798
  • Joined: 18 Dec 2007
  • Loc: Right Coast of the Chesapeake Bay

Posted 12 September 2021 - 05:29 PM

Sorry but that's still confusing. Which of the two positions is best?

It depends on the focal length of the refractor.  But if you can set up your diagonal with and without the barrel, try both ways.  In practice, whichever position gives the flattest-looking field is the best position.  If possible, do your testing with an 80 degree eyepiece.  A 100 degree would be even better.

 

Mike


Edited by Sarkikos, 12 September 2021 - 05:42 PM.

  • Mark9473 likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics