31 replies to this topic

[ols]

Looking for some recommendations please on hopefully a simple new set-up, for short observing sessions on cold winter nights. Cold for here on clear nights is often -10F to 15F. (Northern new england in Bortle 3-4 location) Favorite target is getting a nice look at Jupiter at least before needing to head back indoors to warm up.

 

I already have the new telescope (Tried to get one that is supposed to need less cool down time after my Edge C8 froze over last month. Started looking for a 4” Tak during the sale and only one I could find in stock anywhere was a DZ.) so I now have a 100DZ plus some Maxbright Binoviewers.

 

Where I am getting stuck is regarding what I should use for the simplest combo of GPC and 1.25” eyepieces to get me magnifications up to the 130x-200x range.  When its super cold, I dont want to be changing the set-up too many times. Ideally, I think only 1 GPC and either 2 or 3 eyepiece sets would be great, if that is feasible.  Something along the lines of:
lowest mag 50X range 

normal night max 130X - 150x

best nights max  160x - 200x
 

There are 3 GPCs, 1.25x, 1.7x and 2.6x

I’ve read that Binoviewer eyepieces should ideally be at least 10mm or more

Given the range of lowest to highest mag range I am after, I am also not sure if a Barlow or Powermate would be good to have and where it would go in the optical train or if I’d need one or two? lol

 

If the mount I’d be using matters, I have 2 go-to tracking options (AZ-Gti (which might be too light?) and a Rainbow (the Rainbow (or the external battery) got so cold on the night the Edge froze over, it would no longer slew.)

 

Please let me know what combo of GPC, EP sizes and/or Barlow/Powermate(s?) you’d recommend. Thanks very much for the help 🙏 

[isogroup]

I would target 100x for visual of planets on very cold nights. I used binos at 50x for Jupiter and Saturn for a pleasing 3D look. 200x is the second best mag for a Tak 100 size scope.

 

However, for temperatures below 20, I use a ZWO mount with a telescope and ASI 585MC camera with ASIair for viewing from a warm, indoor location. Just saying...

[Hesiod]

Assuming the DZ has the same focuser of its DL/DF siblings it could reach focus even without GPC (I managed to do so by pairing my Maxbright to the smaller Baader prism); however in my opinion the images look better with the GPC.

 

Personally tend to use the binoviewer mostly for deep sky stuff so usually opt for the 1.7x paired with a couple of 18mm BCOs (ca 70x, a sort of compromise to avoid changing EPs); if want a bit more zoom swap in a couple of 9mm orthos.

 

When set up for planets install the 2.6x and use a couple of Pentax XF12.

 

Note that may increase a bit the multiplying factor by installing the gpc before the diagonal, but can not provide you the exact values (also remember that with the old Maxbright, which is the model I own, the real amplification was a bit lower).

[Spikey131]

I was out in the cold last night with a 130mm f/6.3 refractor.  This has a slightly longer FL than your Tak (820 vs 740).  I virtually always use the Maxbright 2 binoviewers when observing the planets, and I use the 2.6x GPC and a prism diagonal.  It is better optically to use a Barlow or GPC with binoviewers, and avoid eyepieces shorter than about 10mm.  I have a pair of Baader Zoom eyepieces, but my favorites for this setup is a pair of 13mm Nagler T6 EPs.  This yields 164x (in your Tak it would be 148x), and I find this the most useful all around range for the planets.

 

For lower magnification observing, I just take the GPC out or switch diagonals, and use a pair of 24mm Panoptics.  The Pleiades are lovely.  I do not know if your Tak will reach focus without a GPC, but the 1.25x should keep a wide FOV.

Edited by Spikey131, 02 January 2025 - 01:11 PM.

[ols]

Thanks everyone.

@Isogroup - Interesting that you would go for 100x max on cold nights. That makes it easier. I do have a 16x bino (with IS) that is great in cold weather. I also have a Vespera and briefly tried EAA with the Edge C8. Somehow though, I still most appreciate the immediacy of live visual views. Tough to beat for me. When you say 200x is second best mag for this scope, is 100x the best in your view (or a different mag?)

 

@Hesiod  12mm with 2.6x for 170x sounds appealing. I do think a GPC is usually recommended rather than not using one? Do you have any trouble merging the images in the 9mm EPs compared to your 18s?

 

@Spikey131. I had not thought of also possibly swapping out the diagonal. That makes sense rather than trying to unscrew a GPC in the cold.  Your low Pleides mag is roughly 35x without any GPC - is that correct? The focal length of the Tak 100DZ is 800mm. 13mm and 2.6x for 160x also sounds appealing. It sounds like your swap is both diagonal and EPs to go from high to low mag - is that correct?

 

Overall, here is some math for various options still trying to get 3 to mag levels (maybe I should give up on that though and be happy with 2 on cold nights)

 

 

For the 2.6x, it seems like the tradeoff is needing large EP for the lowest mag.
12mm EP roughly 170x
16mm EP roughly 130x
24mm EP roughly 85x
40mm EP roughly 50x. I do have a single 40mm EP that came with the Celestron. Would it be better to aim for 50X or 85X for lowest mag? Would a 40mm 1.25 EP be too wide for any reason (i seem to think 24mm gets the widest view in this set-up so not sure what happens for an EP above that. I’m wrong pretty often though, so not sure)

 

 

For the 1.7x, it seems like an additional Barlow/Powermate pair might be needed for highest mag if EPs should stay above 10mm in a binoviewer
8mm EP roughly 170x
11mm EP roughly 120x
24mm EP roughly 50x

 

adding two barlows just below each EP for changing mags (and keeping same EP) could also be an option?
16mm EP with 2X barlow approx 170x
16mm EP with 1.6X Barlow approx 130x
16mm EP with no barlow approx 85X

 

 

For the 1.25x GPC, it seems definitely need Barlow unless my eyes could merge images with short EPs
5mm EP approx 200X
8mm EP approx 125x
20mm EP approx 50X

24mm EP approx 40x

 

 

Hmm. Maybe I should restart with thinking of 2 magnifications only. Highest and Lowest.  It would be better to only have to swap one thing. If 40x is a good low mag (with 1.25x GPC and 24mm EPs), I could get a high mag of 160x by adding a 4x Powermate below each EP? (This would technically be changing 2 pieces though I guess .) I dont think its possible to add in a Barlow between the diagonal and the binoviewers with a GPC installed.  Any more thoughts most appreciated

Edited by ols, 02 January 2025 - 02:10 PM.

[balcon3]

I have a very similar setup to you, a Tak FC100DF and MaxbrightII binoviewers. First, in case you didn't know this, the 1.7x GPC has been measured at 1.5x and the 2.6x has been found to be actually 2.9x (the 1.25x is accurate at 1.2x). That is when you put them in their usual position between the diagonal and the binoviewer. If placed before the diagonal, they will give somewhat more magnification. I use 2 diagonals when I am observing:  a Baader/Zeiss T2 prism for the binoviewers and a 2 inch mirror diagonal for mono viewing. If you use the binoviewers mostly for planets, then I think the 2.6x (2.9x) GPC is the most convenient. A pair of 12.5x eyepieces would get you to 186x, or 10x would get you to 232x. For medium power, 16mm would get you 145x.  For the low end, 32x Plossls would get you 72x, a bit high for low power, but that's the price for using the high mag GPC. Then for lower powers you could swap in the 2 inch diagonal and view with a nice 2 inch eyepiece. I love my 16mm Masuyama 85 degree eyepiece for binoviewing, since they are ultra sharp, light, and the GPC cleans up the distortions in the periphery of the field. The Masuyama 12.5x (53 degrees) are also great.

Edited by balcon3, 03 January 2025 - 12:05 PM.

[Hesiod]

None, in fact before getting the stronger gpc used 6mm EPs.

[Spikey131]

For the planets, the 2.6x makes the most sense.  If you don’t want to buy a lot of eyepiece pairs, consider the Baader Zooms.  But I could live with just a pair of 13mm Nagler T6 EPs.

 

For low power, the question is whether your system will reach focus without a GPC, and if not, which is the lowest power GPC that will allow you to reach focus.  My AP 130GT will reach focus with a T2 prism diagonal and no GPC, but the Stowaway and TV76 require a 1.25x GPC.  So the widest binoviewer FOV for the 130 and Stowaway are the same, about 2 degrees.  I can see 2.5 degrees with the TV76.

[betacygni]

For cold nights I very much agree with spikey, get some quality zooms. The Baader zooms or APM super zooms. A little bit of sacrifice in image quality (very little) will be made up by them being able to dial in precisely to seeing, less fiddle factor with cold hands, and generally able to observe almost everything without swapping eyepieces.

If on the other hand you want pure performance for planetary, I’d get a pair of Takahashi TPLs, particularly I’d recommend the 18mm with the 2.6x glasspath.

Edited by betacygni, 02 January 2025 - 11:23 PM.

[ols]

Thanks again everyone. So, based on all the input above, I think my question has evolved into: is there an EP solution where I only need to make one change to go from a low power mag that will frame the Pleides, to a high power mag that will give good magnification for Jupiter?

 

The double zoom idea is a good one (I tried one in the past) but not sure about being able to twist both barrels accurately in the cold (so both on the same setting, my recollection is that the detentes were tricky to feel where to stop, especially with gloves on) while also not accidentally changing the IPD amount? 

 

I did not realize the actual GPC mags have been measured as different to Baader’s labeling, but hopefully using their official 1.25x, 1.7x and 2.6x figures for approximate calculations is still close enough.

 

For figuring out low mag, I decided to use astronomy.tools to see how various EP sizes would frame the Pleides assuming each GPC as the Barlow size (they dont have every exact GPC multiplier but again, hopefully close enough.) Takeaway was that 24mm EP (tried Panoptic as suggested above) seemed to be best choice, but only with the 1.25x GPC (widest view, ~40x) or 1.7x GPC (tighter view, ~55x, but Pleides still seems to just fit)  The highest 2.6x GPC was just too narrow, at least per astronomy.tools

 

For high mag, looking at suggestions above and trying not to have to switch GPC or diagonals, the math seems to work out well for 16mm 85degree Masuyamas, each with a 2.5x Powermate? (Pretty close magnification to the 13mm Naglers with a 2.6x GPC you like above)

 

 

So, potential solution would be to install 1.25x GPC in binoviewer side of diagonal. Start off with 24mm EP for low power (make sure scope aligned with finder, view Pleides, etc.) When ready, can make switch to high power view by swapping out 24mm EPs to 16mm Masuyamas that are already attached to 2.5x Powermates for 150x. (0.75 exit pupil.)  Could also just add 2.5x Powermates below the 24mm EPs for 100x

 

Another option would be 24mm EPs low power, and then 6mm EPs high power. This would be lighter weight for high power but still unclear to me whether 6mm EPs or 16mm+2.5x Powermate would have a better view, preferable eye relief or be easier to merge?

 

I really appreciate the suggestions. Thanks again

Edited by ols, 03 January 2025 - 10:50 AM.

[balcon3]

I have tried all of the things that you are trying to do with my FC100DF. First, I think your calculations with astronomy.tools are a bit off.   The Pleiades are about 1.8 degrees in size. In my scope and experience, the only binoviewer setup that will include the whole cluster is without any GPC, which gives a 2.1 degree TFOV. Even the 1.25x GPC gives a 1.7 degree TFOV, and that is in my f/7.4 scope. In your f/8 the field of view will be a bit narrower, about 1.6 degrees. And you will want some extra space around the cluster for framing. So one solution for big clusters like the Pleiades is to not use any GPC, assuming your DZ can reach focus without a GPC. You would just get the whole cluster into the field of view. Personally, for the Pleiades and other larger clusters, I prefer to remove the bino-viewer and use a 2-inch eyepiece in mono mode. If you have 2 diagonals, its easy to remove the bino-viewer and diagonal as a unit and slip in the 2-inch diagonal.

 

I have not tried to add Barlows in front of the eyepieces on a binoviewer. I imagine the system could get quite back heavy, so it depends on your mount. I have trouble using low FL eyepieces with short eye relief on binoviewers. Even eyepieces that I can use fine in mono mode, like BCO 6mm or Masuyama 10mm (85 degrees), I can't get both eyes close enough to the eyepieces to see the whole field in bino-mode.  Your face might be built differently and it might be OK for you. For me, the best way to view planets is with a GPC or Barlow between the diagonal and the binoviewer.

[betacygni]

I’ve never observed in cold as bad as yours, but with relatively thin gloves I’ve not had an issue zooming. In any event I suspect finding equal zoom settings would still be vastly easier than attempting to swap eyepieces, diagonals, or GPCs with gloves. As for IPD, no I’ve never had them effect this zooming (though maybe in extreme cold they don’t zoom quite as smoothly if grease stiffens up).

Another option that I think would actually be best for you, but require a large gear change, is to buy a pair of Denkmeier Binotrons with the powerswitch. 1.3x, 2.3x, and 3x with the pull of a lever. This would be worth considering before investing too much in GPCs, powermates, different eyepieces, etc.

[ols]

Ha, it would be typical for me to mess up using something like astronomy tools.

I re-entered my info and for my 800mm F8 scope and a 24mm Televue Panoptic (which I’ve read gives the widest possible 1.25” FOV?), I get 2.04 degrees FOV for no GPC and 1.77 degrees for a 1.15x GPC (they dont have a 1.25x option) Hopefully either of those would be close enough on the Pleiades? The no GPC option definitely seems better for low power FOV though. 

I also re-read the Maxbright manual and it says no GPC at all should be needed for scopes slower than F/7, so theoretically I should be OK without.   I am just not knowledgeable enough to know what the issue could be to not reach focus without a GPC (would I have to add more spacers between the focuser and the diagonal or… take some out? I’ve seen the GPC’s described as having negative optical length, so I assume the answer is take some out? - just not sure.). Assuming I can reach focus without any GPC, a possible solution would then be:

-24mm EPs (no GPC at all) for low power widest setting

-5mm EPs (or some powermate/barlow EP combo like 16mm with 3x barlows) for ~150x

 

Meanwhile, switching to those Denkmeiers with the  powerswitch for sure seems like it could be ideal since I’m really just after the easiest way to switch from lowest to highest power when its cold. (I will need to do some research to see if one of the magnification options is just 1x?) One of the things I’ve learned on cloudynights is that I’ve almost never had a question that wasnt asked before so there is probably already at least one thread on Denkmeiers with a 4” refractor.

 

Hmm. My question here seems to have turned out to be more of a binoviewer question than the eyepiece question I thought it was. Maybe I should ask the moderator to move it. 
 

Thanks again for the helpful replies!

Edited by ols, 03 January 2025 - 04:18 PM.

[balcon3]

Ha, it would be typical for me to mess up using something like astronomy tools.

I re-entered my info and for my 800mm F8 scope and a 24mm Televue Panoptic (which I’ve read gives the widest possible 1.25” FOV?), I get 2.04 degrees FOV for no GPC and 1.77 degrees for a 1.15x GPC (they dont have a 1.25x option) Hopefully either of those would be close enough on the Pleiades? The no GPC option definitely seems better for low power FOV though. 

I also re-read the Maxbright manual and it says no GPC at all should be needed for scopes slower than F/7, so theoretically I should be OK without.   I am just not knowledgeable enough to know what the issue could be to not reach focus without a GPC (would I have to add more spacers between the focuser and the diagonal or… take some out? I’ve seen the GPC’s described as having negative optical length, so I assume the answer is take some out? - just not sure.). Assuming I can reach focus without any GPC, a possible solution would then be:

-24mm EPs (no GPC at all) for low power widest setting

-5mm EPs (or some powermate/barlow EP combo like 16mm with 3x barlows) for ~150x

 

Meanwhile, switching to those Denkmeiers with the  powerswitch for sure seems like it could be ideal since I’m really just after the easiest way to switch from lowest to highest power when its cold. (I will need to do some research to see if one of the magnification options is just 1x?) One of the things I’ve learned on cloudynights is that I’ve almost never had a question that wasnt asked before so there is probably already at least one thread on Denkmeiers with a 4” refractor.

 

Hmm. My question here seems to have turned out to be more of a binoviewer question than the eyepiece question I thought it was. Maybe I should ask the moderator to move it. 
 

Thanks again for the helpful replies!

The issue about not reaching focus without a GPC in some scopes is that the binoviewer adds alot of length to the telescope. In some scopes, you can't rack the focus in far enough to reach focus. If anything, you would have to remove sections in order to reach focus, but in some scopes you don't have to, and in other scopes there is nothing to remove so it's impossible. Adding a GPC pushes the focal point outward (adds length to the light path), allowing you to reach focus. One issue with the Denkmeyer with the Powerswitch is that it is thicker than the Maxbright II. Therefore in some scopes you might not be able to use the Denk 1x setting. Hopefully someone with experience will be able to comment on whether a Denkmeyer will reach focus at 1x on a FC100DZ. 

[mikeDnight]

Looking for some recommendations please on hopefully a simple new set-up, for short observing sessions on cold winter nights. Cold for here on clear nights is often -10F to 15F. (Northern new england in Bortle 3-4 location) Favorite target is getting a nice look at Jupiter at least before needing to head back indoors to warm up.

 

I already have the new telescope (Tried to get one that is supposed to need less cool down time after my Edge C8 froze over last month. Started looking for a 4” Tak during the sale and only one I could find in stock anywhere was a DZ.) so I now have a 100DZ plus some Maxbright Binoviewers.

 

Where I am getting stuck is regarding what I should use for the simplest combo of GPC and 1.25” eyepieces to get me magnifications up to the 130x-200x range.  When its super cold, I dont want to be changing the set-up too many times. Ideally, I think only 1 GPC and either 2 or 3 eyepiece sets would be great, if that is feasible.  Something along the lines of:
lowest mag 50X range 

normal night max 130X - 150x

best nights max  160x - 200x
 

There are 3 GPCs, 1.25x, 1.7x and 2.6x

I’ve read that Binoviewer eyepieces should ideally be at least 10mm or more

Given the range of lowest to highest mag range I am after, I am also not sure if a Barlow or Powermate would be good to have and where it would go in the optical train or if I’d need one or two? lol

 

If the mount I’d be using matters, I have 2 go-to tracking options (AZ-Gti (which might be too light?) and a Rainbow (the Rainbow (or the external battery) got so cold on the night the Edge froze over, it would no longer slew.)

 

Please let me know what combo of GPC, EP sizes and/or Barlow/Powermate(s?) you’d recommend. Thanks very much for the help 🙏 

I have a GPC and find it a bit of a fiddle to use. I much prefer using a 2X Ultima SV barlow with my Maxbright and FC100DZ. The barlow gives an approximate 4X amplification when attached to the nose of the binoviewer which enables the use of some long focal length eyepieces which makes observing very comfortable. I'm mainly a lunar and planetary observer and find that my 35mm, 25mm and 18mm 5 element Ultima's give a great range of magnifications. I have bingo pairs of Ultima's down to 7.5mm but rarely ever find I need the 12.5mm's, 10mm's & 7.5mm's, although I do like a pair of 16.8mm orthoscopic's that I've had for years.

Occasionally I've used a Tak 1.6X extender-Q as well as a 2X barlow for Lunar. Extreme high powers through the DZ and binoviewer when viewing the moon can be jaw-dropping. No tiny eye lenses for me!

 

FC100DZ with extender-Q and 35mm Ultima's

[balcon3]

One more comment. I think most people who start binoviewing go through a period where they work out their system. It's not plug-and-play like mono-viewing. As you are finding out, many parameters come into play. The trickiest part is how to switch out GPC's or Barlows if they are placed in their standard location between the diagonal and the binoviewer. Switching GPC or Barlow means dismantling the system, switching the GPC or Barlow, and then putting it back together again. It can be done, but I wouldn't want to do it often in a session, and not on a cold night. So various solutions have been devised to deal with this issue. One is the Denkmeyer with the Powerswitch. Some people use a Baader Quickchange system to make dismantling and reassembling the system easier. Some use Barlows after the binoviewer, where they are easier to switch. Some have two diagonals with different GPC's installed (or one with GPC and one without). Some stick with a low mag  or no GPC and use really short focal length eyepieces for planets. And some, despite it all, do switch GPC's or Barlows by taking apart the system and putting it back together. It's all doable, but it takes a bit of experimentation to find out what works best for you and your viewing preferences. My current personal solution is to do all my planet viewing at the beginning or the end of the session with the 2.6x GPC installed. When not viewing planets, I install the 1.25x GPC and switch back and forth between binoviewing and mono viewing by switching out diagonals, which I find to be pretty painless.

[betacygni]

The lowest magnification option on the powerswitch is about 1.3x. If this can’t get you the FOV you want I’d honestly just look into getting binoculars for those few objects. At these apertures they make more sense for wide fields (a 50mm binocular will give close to the brightness of a 100mm refractor binoviewed, a bit larger binocular would equal it). Or as much as it pains me to say, just stick a mono eyepiece into the focuser for those few really wide objects.

Edited by betacygni, 03 January 2025 - 05:11 PM.

[MJB]

I've got an FC-100DZ and an early Denkmeier BV.  The BV is coupled with a Baader T2 prism diagonal and a 2.6 GPC. I needed a GPC to reach focus. My eyepieces are mainly Morpheus 17.5mm (very nice, but about the outside limit for weight), Celestron 26mm  silvertops, and some Tak 12.5 and 9mm orthos. If I had to do it over again, I'd get a Denk Binotron with a powerswitch - that would seem to offer the most convenient solution. Swapping out eyepieces isn't too much of a problem with the lighter items, but the Morpheus require a bit more fiddling to change out. In any case, binoviewing for lunar and planetary has been a quantum leap in viewing enjoyment for me. 

[ols]

Thanks again all.
As a next step, I’m going to see if I can reach focus without any GPC using the Maxbrights and the 100DZ. 

 

My approach is to figure out my target backfocus, based on Takahashi’s visual system chart for the 100DZ in mono mode, and then see how close I can get with adapters between the 100DZ and the binoviewers. Does this approach make sense?

 

Here’s what I’ve got so far. If I follow the Tak Visual System chart for each part recommended to monoview with 1.25” EPs using Tak’s 2” diagonal, the total optical length is 172.5mm.  (It would be 161mm if using 2” EPs) First number is the optical length

15mm - TKP19001 - M64 Tak focuser to M72 thread adapter

40mm - TKP 27110 - 2” EP adapter

106.5mm - TKA00543 - 2” Diagonal

11mm - TKA00111 -  50.8 to 31.75 reducer to allow 1.25” EPS

 

Hunting around for adapters, the shortest assembly I’ve been able to figure out so far to connect Maxbright binoviewers is 174mm. I think I could actually connect everything in 159mm, but probably really need the 15mm Baader quick change system in there to make sure I can adjust the diagonal to point the right way.

8.5mm - Baader 2458231 (M64x.75 male thread (to connect to end of Tak focuser tube) to M68 female thread)

5.5mm - Baader 2458233 (M68 male thread to T2 male thread)

15mm - Baader 2456322 Heavy Duty quick changer (T2 female thread on quick changer side and T2 male thread on change ring side)

35mm - Baader 2456005 T2 Prism Diagonal (their shortest optical length Diagonal?)

110mm - Maxbright binoviewers

 

If the above is based on incorrect assumptions or otherwise seems like it probably wont work, please let me know! 
otherwise I will order some adapters. 
thanks again

Edited by ols, 05 January 2025 - 11:11 AM.

[mikeDnight]

For the DZ with maxbright & 1.25" BBHS Prism

[ols]

Thanks
That also looks like a good solution. And it is great to know that it should work! 

I calculate that optical length, between the end of the focus tube and the diagonal, to be 37.4mm

15mm - TKP 19001 - M64 Tak focuser to M72 thread adapter

10mm - Baader 2558230 - M72/M68 Adapter

12.4mm - Baader 2458231 ultrashort 2” clamp

 

For the parts I posted just above, I get an optical length of 29mm to the diagonal? 

8.5mm - Baader 2458231 (M64x.75 male thread (to connect to end of Tak focuser tube) to M68 female thread)
5.5mm - Baader 2458233 (M68 male thread to T2 male thread)
15mm - Baader 2456322 Heavy Duty quick changer

 

Hopefully i can go with either one and can make a choice based on whatever is in stock

[Kunama]

My DZ is set up as:ng 

 

DZ draw tube + M64 Clicklock + T2 Maxbright Diagonal + Maxbright II binoviewer   
OR alternately

DZ draw tube + M64 Clicklock + T2 Maxbright & GPC1.25x + Zeiss Primo binoviewer 

 

both setups come to focus with the drawtube racked out about 10mm

 

being predominantly a lunar/planetary observer, my eyepiece kit consists of five pairs of Takahashi LEs ( 5, 7.5, 12.5, 18 & 30mm)

Edited by Kunama, 06 January 2025 - 02:36 AM.

[ols]

Thanks again everyone. 

For the low magnification set-up, I now have adapters ordered to try to reach focus with no GPC (and use 24mm EPs)

 

For switching to higher power, I am trying to figure out how it would work if I switched in a different diagonal with a 2.6x GPC installed on the binoviewer side (I would be switching out the no GPC diagonal in this scenario) 

 

question 1

Baader says the focus gain of a 2.6x GPC after the diagonal is approx 65mm. Does this mean that I should also ideally have 65mm in extensions mounted on the telescope side of the new diagonal with 2.6x GPC installed (to keep the backfocus as similar as possible)?

If you are swapping in a diagonal with a different GPC, does it also have any extensions installed?

 

question 2

I have read several cloudynights threads that discuss mounting placement for GPCs. Does everyone generally use GPC after the diagonal? If you are placing the GPC elsewhere, how is this better for your specific set-up?

 

option1. Generally, placing the GPC on the binoviewer side of the diagonal is recommended first.

 

option 2. Mounting to the telescope side is also done, and seems to slightly increase magnification compared to option 1. Also, some suggest that, if using a Prism diagonal, that could be the preferred location to help most with correction

 

option 3. Not sure if anyone has done this (and whether Baader actually says dont do it?) but I have also read some discussion on having 2 GPCs that could be mounted at the same time, in each location on one diagonal. The magnification would then be the product of the 2 GPCs. E.g., 2.6 x 1.7 =4.42 ?  (not sure how much focus gain from this if this works)

 

I will definitely try option 1 first, but I am also interested to know if anyone has tried option 3? 

Edited by ols, 07 January 2025 - 02:59 PM.

[balcon3]

Thanks again everyone. 

For the low magnification set-up, I now have adapters ordered to try to reach focus with no GPC (and use 24mm EPs)

 

For switching to higher power, I am trying to figure out how it would work if I switched in a different diagonal with a 2.6x GPC installed on the binoviewer side (I would be switching out the no GPC diagonal in this scenario) 

 

question 1

Baader says the focus gain of a 2.6x GPC after the diagonal is approx 65mm. Does this mean that I should also ideally have 65mm in extensions mounted on the telescope side of the new diagonal with 2.6x GPC installed (to keep the backfocus as similar as possible)?

If you are swapping in a diagonal with a different GPC, does it also have any extensions installed?

 

question 2

I have read several cloudynights threads that discuss mounting placement for GPCs. Does everyone generally use GPC after the diagonal? If you are placing the GPC elsewhere, how is this better for your specific set-up?

 

option1. Generally, placing the GPC on the binoviewer side of the diagonal is recommended first.

 

option 2. Mounting to the telescope side is also done, and seems to slightly increase magnification compared to option 1. Also, some suggest that, if using a Prism diagonal, that could be the preferred location to help most with correction

 

option 3. Not sure if anyone has done this (and whether Baader actually says dont do it?) but I have also read some discussion on having 2 GPCs that could be mounted at the same time, in each location on one diagonal. The magnification would then be the product of the 2 GPCs. E.g., 2.6 x 1.7 =4.42 ?  (not sure how much focus gain from this if this works)

 

I will definitely try option 1 first, but I am also interested to know if anyone has tried option 3? 

Regarding question 1:  On a refractor, there is no need to have the binoviewer with and without the GPC come to focus in the same place. It can be convenient, but it has no optical significance. So if your focuser has enough travel to be able to reach focus without a GPC (racked in) and also without a GPC (racked out), you don't need to use an extension tube. However, 65mm is a lot of back focus, so it is likely that you will need some kind of an extension tube to let you reach focus with the 2.6x GPC. But it doesn't have to be 65mm. It can be whatever length allows you to reach focus. I use a 35mm extension in my FC100DF when I use the 2.6x GPC and it works fine. I think that your DZ came with a 35mm extension. You can use that.

[ols]

Original poster here with a brief update. I received the Baader adapters I ordered (plus some EPs) and the Binoviewers came to focus no problem. Thanks everyone for the help!  I am still trying to figure out the easiest single change (with gloves on, ha) from lowest magnification mode to high magnification mode.

 

In the meantime though, i did find where Baader indeed does not recommend using 2 GPCs together (my option 3 above.) The following is in the Q&A section of Baader’s website for the 2.6 GPC:

 

Is it possible to stack GPC's without losing image quality?

For example, a 1,25x or 1,70 GPC on top of the 1,7x newtonian GPC with a Mark V binoviewer. That would give a nice flexibility.
Saul / January 18, 20171 Answer
Sorry, GPCs are not designed to be stacked. Dual stacking will create spherical aberration - unfortunately we cannot recommend it.
Baader Web Team / January 19, 2017

 

I then decided to submit a question to Baader directly about using the GPC before or after the diagonal. Baader says that placing the GPC after the diagonal is the corrct choice. Here is their reply:

 

Your Question:
I am using a T2 Prism diagonal with Maxbright binoviewers. Since both have a prism, and the GPC is meant to correct prism color aberrations, is the correction any better if the GPC is mounted before the diagonal compared to after the diagonal? Or does it make no difference? (I understand the magnification will not be the same for a GPC mounted in each location.) Thank you

Answer(s):
This would theoretically/practically be possible, but it makes almost no sense. The glass path corrector should be installed in front of the bino to prevent vignetting. That is much more important in our opinion and visually noticeable.
Baader Web Team
21.01.25

Edited by ols, 21 January 2025 - 07:18 AM.