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Any thoughts on replacing "stock" with 1 1/4" or 2" diagonal?

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#1 SimonMiller

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Posted 24 January 2020 - 12:05 PM

I have a new Sky-Watcher HEQ5 equatorial mount and EdgeHD 800 SCT OTA which includes a 40mm Celestron "Plossl" eyepiece with 43 degree FOV. I have just bought a range of B-H Hyperion eyepieces which fit a 1 1/4" diagonal but also have 2" barrels. Rookie mistake No. 1 - assume they would "just" work with existing diagonal!

 

The first issue: the screws on the diagonal have heads that sit higher than the barrel and the wider design of the B-H EP don't sit flush - they are sitting up by about 3mm (1/8").

 

The second issue: the screws will either get caught on the undercut (and probably "mark" the sides of the barrels which I would like to avoid) or just be a pain to operate.

 

One solution is to "junk" the new but entry level mirror diagonal - for the price it's probably OK but there's a feeling that it's probably going to "let the side down" so will be heading out the door before too long anyway. There's a million and one diagonals available but I'm seriously considering:

  1. 1 1/4" Celestron dielectric #93571 push-fit
  2. 2" Celestron dielectric (with 1 1/4" adapter) #93573 with SCT and push-fit adapters

Both have a twist-lock, but they obviously have different features:

  • 1 1/4" uses visual back (two screws hold it in place)
  • 1 1/4" has threads for 1 1/4" filters but 2" has "only" 2" threads (not on 1 1/4" adapter)
  • 2" screw on to SCT back (replacing the visual back)
  • 2" push-fit into a 2" focuser e.g. on many refractors

So my (dumb) question is what are the pros/cons for operating (living with) either type? The two screws in visual back would allow easy adjustment of the viewing angle? The SCT connection could come loose with a v. heavy 2" EP as the telescope slews? I have no experience of either type (current OTA has rotary focuser with nylon screws). Operation of both in a cold environment?

 

The extra weight of the diagonal for the mount wouldn't be an issue (extra 350g) and there's no problem with clearance.

 

I did read that the EdgeHD is "optimised" for 1 1/4" diagonals - get spherical distortion if focal point is moved too much. I estimated  that the optical path is longer through the 2" back by about 6cm or 7cm, but as the visual back isn't needed 7cm is saved (so by design or accident) it's about/almost the same. So, it might be an issue with a 2" push fit used with a visual back e.g. longer optical path through the bigger diagonal plus length of a visual back?

 

FWIW I don't have immediate plans to buy the 0.7" focal reducer. It's not definite that I will go "long" because I might get a 2nd shorter FL OTA. I also have a Newtonian (which I will probably sell) so wider views are something that I would eventually want to reinstate.

 

Lastly, a question about the B-H Hyperion EP (unmodified) - can the 2" barrel straight in the 2" diagonal or will the 1 1/4" adapter always be needed?

 

Simon



#2 Jeff Struve

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Posted 24 January 2020 - 12:10 PM

I replaced the visual back with a Baader Clicklock... now I can use a standard diagonal that is easy to adjust without the fear of the visual back threads being loosened by the weight of the eyepiece...


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#3 sanbai

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Posted 24 January 2020 - 12:30 PM

My vote is also for a collet mechanism (=twistlock, clicklock, rotolock...) for both the visual back and the diagonal. I have the Baader clicklock visual back for my C8edgeHD (offers shows up from time to time in the classifieds) and also a Baader diagonal with clicklock. I'm considering replacing the diagonal that has a compression ring for a Baader one, just for this feature.

 

I don't know, but the direct attachment of the diagonal into the threaded output of the SCT may bring the eyepieces too close to the scope. Remember that the C8edge has some nuts around that may interfere with the eyepiece when rotating the diagonal. Just check.

 

I don't know how comfortable/safe is to rotate the diagonal a bit for visual comfort using the direct thread method. I know that with the Baader clicklock there is no issue at all, it's easy to unlock and lock again.

 

I would not worry for the extra optical path. The focuser can cope with that easily, and for visual use it doesn't really matter. My optical path is quite large because I added a filter slide to my 2" diagonal. It may be one of the longest optical paths possible! (a filter wheel would be a tad longer). The actual backfocus distance is more important for astrophotography, but then your set up would be different anyway.

 

BTW, make sure the diagonal can accept filters. It's easier to swap eyepieces if the filter stays in the diagonal.

 

Santiago



#4 Spikey131

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Posted 24 January 2020 - 02:38 PM

1.  If your current eyepieces are all designed for both 1.25 and 2” diagonals, you don’t need a 2” diagonal.  They should work in your 1.25” unit.  But it sounds like a 2” would work better with the ones you have.

 

2.  There are eyepieces that are 2” only, ones with longer focal lengths, e.g. a 55mm Plossl.  These wide field EPs have a field stop greater than 1.25” and will not fit.

 

3.  Besides accommodating 2” EPs, a reason to upgrade to a 2” diagonal and visible back is the physical strength of the connection which is helpful with large heavy eyepieces and cameras.

 

4.  For visual use with a single eyepiece (as opposed to binoviewers), you do not need to concern yourself with the extended optical path of a 2” diagonal.  It will not cause noticeable distortion.

 

5.  What I did for my C8 is a Baader Clicklock visual back and a Baader Clicklock 2” mirror diagonal.  I like the security of the Clicklock system and it was worth the cost to me.  



#5 SimonMiller

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Posted 24 January 2020 - 02:53 PM

My vote is also for a collet mechanism (=twistlock, clicklock, rotolock...) for both the visual back and the diagonal. I have the Baader clicklock visual back for my C8edgeHD (offers shows up from time to time in the classifieds) and also a Baader diagonal with clicklock. I'm considering replacing the diagonal that has a compression ring for a Baader one, just for this feature.

 

I don't know, but the direct attachment of the diagonal into the threaded output of the SCT may bring the eyepieces too close to the scope. Remember that the C8edge has some nuts around that may interfere with the eyepiece when rotating the diagonal. Just check.

 

I don't know how comfortable/safe is to rotate the diagonal a bit for visual comfort using the direct thread method. I know that with the Baader clicklock there is no issue at all, it's easy to unlock and lock again.

 

I would not worry for the extra optical path. The focuser can cope with that easily, and for visual use it doesn't really matter. My optical path is quite large because I added a filter slide to my 2" diagonal. It may be one of the longest optical paths possible! (a filter wheel would be a tad longer). The actual backfocus distance is more important for astrophotography, but then your set up would be different anyway.

 

BTW, make sure the diagonal can accept filters. It's easier to swap eyepieces if the filter stays in the diagonal.

 

Santiago

Thanks - "full marks" for your five good points.

 

1. Both options have a twist lock for the diagonal-eyepiece. For 2" diagonal there is a push fit use with diagonal-Baader click lock.

 

2. The 1 1/4" slips into a visual back that's 7cm long so has good clearance. The 2" sits closer, I estimate the EP will be 3cm closer to the back  of the OTA. So clearance is reduced from about 12cm to 9cm - that's OK and the knobs stick out about 4cm. On a C14 you would need more clearance but for C8 that seems OK as EP are relatively long and OTA diameter is relatively small.

 

3. Rotating the diagonal was my concern. If it's too tight then releasing it would disturb the OTA, but too loose and it risks the EP rotating it. I  guess there is a point that works but a Baader click would help with the 2" and the option to use the 2nd adapter for a push-fit helps achieve this. Using screws and a visual back to hold the diagonal was the 1 1/4" option that. would be easy to operate but might need attention to ensure diagonal is pushed into visual back unlike the 2" that pulls itself together as the nut is tightened.

 

4. Extra optical path was only a concern because I originally thought the 2" diagonal was so large that the path was much longer but I later realised that the visual back isn't used with a direct SCT so the paths are not dissimilar (in fact they may be identical because they are "known" quantities when using Celestron's own diagonal and mounting method.

 

5. I have a moon filter that's 1 1/4" - it would fit on the back of the 1 1/4" diagonal. On the 2" diagonal a different filter is required. It's not obvious if the back of the 1 1/4" adapter is also threaded. At least it has a stop to prevent an eyepiece going in too far - so there is the potential to drop a filter in. Lastly I could put the filter on the eyepiece however at least one of the eyepieces has the rear element closer than the length of thread on the filter. A B-H filter may have less thread to solve this problem. So for the moon the 24mm has lots of space but the 21mm not much. Other EP are somewhere in between. Perhaps it's OK to leave the filter a couple of turns on without too much risk of it coming off and it can't fall through into the diagonal because of the stop.

 

I replaced the visual back with a Baader Clicklock... now I can use a standard diagonal that is easy to adjust without the fear of the visual back threads being loosened by the weight of the eyepiece...

Thanks - Baader Clicklock is something I'm looking at - for now it's been a (relatively) expensive month: mount, OTA, EPs, power, head torch, table so this would be something for the future.

 

The OTA has 2" SCT thread but there is a bigger nut behind it 3.25". Not sure if this one is compatible as Baader suggest the 3.25 is for 9.25 OTA or above.

 

I'm seriously considering:

  1. 1 1/4" Celestron dielectric #93571 push-fit
  2. 2" Celestron dielectric (with 1 1/4" adapter) #93573 with SCT and push-fit adapters

Perhaps I could have asked my question more directly, I wanted to compare the operation of these two diagonals. However I'm coming around to the idea that the B-H diagonals with click-lock are probably the way to go.

 

Is it likely that the SCT nut holding diagonal will come undone? My EPs weight at most 500g. A diagonal can weigh 500g too but it's not putting the same force on the nut. A big EP like Explorer Scientific 68 degree 40mm weighs 1000g - perhaps this is the point where things start to unwind?

 

Simon


Edited by SimonMiller, 24 January 2020 - 07:03 PM.


#6 SimonMiller

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Posted 24 January 2020 - 03:33 PM

1.  If your current eyepieces are all designed for both 1.25 and 2” diagonals, you don’t need a 2” diagonal.  They should work in your 1.25” unit.  But it sounds like a 2” would work better with the ones you have.

2" might not accommodate the longer part off the BH-H EP? It has a 2" barrel and negative elements within a lower part that's 1 1/4". For some diagonals this might be a problem...

 

Here's a picture of how the EP can be used. The stop ring is 7mm thick and the extension is 14mm. I'm not intending to use either - but you get the picture...

 

Screenshot 2020-01-24.jpeg

 

So this implies (to me) that without either of these extras the clearance would be increased by another 7mm. So it should be possible to use at least this diagonal and probably the one I'm looking at without needing to use the 1 1/4" adapter?

 

FWIW I like B-H stuff because the publish lots of specs on their websites and have examples of how to use stuff (as above). Their specs varies for each EP and show that the 2" section is about 23mm and the 1 1/4" is about 24-28mm long (this part wouldn't usually be on a 2" EP). The total length of barrel for 2" and 1 1/4" sections is 43-51mm long. Of course  the overall length may still be too much.



#7 MikeMiller

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Posted 24 January 2020 - 04:29 PM

I sometimes forget that the EdgeHD 8 comes with a 1.25" diagonal. It is absurd not to make use of the wide fields the flattener provides. Without the clicklock it would not be my favorite scope for visual.



#8 SimonMiller

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Posted 24 January 2020 - 05:24 PM

I sometimes forget that the EdgeHD 8 comes with a 1.25" diagonal. It is absurd not to make use of the wide fields the flattener provides. Without the clicklock it would not be my favorite scope for visual.

Thanks Mike, you probably have the exact same B-H setup that I'm considering on your EdgeHD. You almost certainly have better sky/weather conditions than we have in the UK.

 

I'm coming around to the idea that a 2" diagonal is the way to go with the Clicklock system. The B-H mirror diagonal is slightly less expensive than the Celestron diagonal but requires the SC-Clicklock so it's a bit more expensive overall. I'm thinking a complete B-H solution would be best.

 

The answered question from their website:

 

"I have a Celestron Edge HD 8" SCT. After a few months using the 40mm kit eyepiece, I'm looking to purchase a couple of Hyperion eyepieces. What ClickLock components would be required to mount this?

 

To use 2"-accessories with an SCT or EdgeHD, we recommend the following parts:
#2956220 SC-Clicklock (for 6", 8", 9¼") or #2956233 SCL-ClickLock (11", 14")
#2956100 Baader 2" ClickLock Diagonal Mirror or #2456115 Baader 2" BBHS ® Mirror Diagonal with 2" ClickLock Clamp
optional: #2956214 Baader 2" to 1¼" ClickLock Reducer (T-2 part #15B) (all Hyperion an Morpheus eyepieces can be used with the 2" barrel; this reducer is only necessary for 1,25" eyepieces)".

 

I don't need the 1 1/4" adapter according to B-H website for my Hyperion EP.

 

I think Celestron didn't do their EdgeHD customers any favours giving them a 1 1/4" diagonal. Perhaps they realise that these customers will flip to the B-H "dark side" at the first opportunity and so don't try to compete. It's almost like they want you to "bin" the supplied EP and diagonal...


Edited by SimonMiller, 24 January 2020 - 07:05 PM.


#9 MikeMiller

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Posted 26 January 2020 - 10:25 PM

Yeah, that is the exact setup I have.

While the Morpheus doesn't need a 1.25-2" adaptor, other 1.25" eyepeices do. I like the Clicklock one, but it is expensive as these things go. If you don't need it or want to reduce costs, you can go with a cheaper adapter.

On thing about Celestron including a 2" diagonal is that it would make the scope cost more, and be vastly inferior to a Baader diagonal. So, it is kind of better this way.

#10 SimonMiller

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Posted 28 January 2020 - 07:50 PM

On thing about Celestron including a 2" diagonal is that it would make the scope cost more, and be vastly inferior to a Baader diagonal. So, it is kind of better this way.

I agree, I’ve purchase the Baader 2” SCT Clicklock and the separate Baader 2” mirror diagonal. I’ve also ordered the Hyperion 36mm Aspheric which gives a true wide FOV (as 2” EP). So all my Hyperion EP will fit directly in the 2” diagonal. There is also space for one EP filter.

 

One interesting fact about Hyperion EP, is that the reference plane and reference focal plane is the top of the 2” part of barrel. Putting these EP directly in the diagonal avoids the depth of an adapter and the length of the 2” part of the barrel.This increased height increases the back focus unnecessarily and also pushes the F/L up 3x extra height and so is best avoided. In contrast, the Morpheus EP have their focal plane at the top of the 1 1/4” barrel. So these EP are optimised for use in a 1 1/4” diagonal but also in a 2” diagonal where the extra height saved compensates for the extra path length of the bigger diagonal.

 

Simon 


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#11 SimonMiller

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Posted 29 January 2020 - 08:08 PM

It's off my own topic/thread, but my Aspheric EP, Clicklock and Diagonal arrived today and also a 2" Baader Planetarium ND0.95 filter. These filters are not inexpensive but seem to be made to a higher quality than many others. I will be using it for visual observation of the moon (when it ceases to be cloudy and the rain goes away). I did plan to get the 1 1/4" one for my Hyperion EPs (24mm and lower) that I will view the moon with, but somehow I ordered the 2" version that "fits" the diagonal instead. It's certainly convenient to fit a filter on the diagonal however...

 

The preferred location for a filter is normally "quoted" as being close to the focal plane of the EP, hence the position of threads for filters, but they can be used on the diagonal, hence the location of threads on the diagonal too. On this diagonal there is also an additional 2" thread closer to the mirror.

 

BH make a statement that all filters show their inherent defects more as they are moved away from the focal plane of the EP. Are there any "performance penalties" in using this particular 2" filter on the diagonal instead of the EP filter threads e.g. having a 1 1/4" version for the Hyperion EP that are 24mm (or less) when visually looking at the moon?

 

What are examples of filters that can be placed on the diagonal thread closest to the mirror - it's not so easy to get this compared to the other end of the nose?

 

Can the suggestion that the "best" place mostly be ignored especially if they are "planeoptically polished". BH say "Phantom Group coated. No ghosting, reflections or stray light". I might have a bit of OCD, so it's easy to obsess about 1/10 wavelength dielectrics etc. and then forget that filters (almost anything optically) and their location also make a difference - the problem being that "good ones" also tend to be "expensive" so can (conveniently) be easily overlooked!

 

Simon



#12 SeattleScott

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Posted 29 January 2020 - 09:42 PM

Interesting, hadn’t heard that about filters before. Honestly sometimes I just hold them up in front of the eyepiece. Especially if I am trying to gauge the effect of the filter. Works fine.

Scott
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#13 MikeMiller

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Posted 30 January 2020 - 02:01 PM

I have never heard of "performance penalties" based on the position of the filter, and I suspect these don't apply to ND moon filters. It probably applies to only narrowband filters and maybe only for photography. On most camera lenses the filter goes in front of the lens, and it works just fine, I would expect the same to apply here.

 

I do use my 2" adjustable polarizing and UHC filters on the threaded nosepeice of the ClickLock Diagonal (the end that goes in to the scope). It is convenient when observing and changing between 2" and 1.25" eyepieces.

 

Just don't forget to take the ND filter off when slewing away from the moon. :)



#14 SimonMiller

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Posted 03 February 2020 - 04:50 PM

I have never heard of "performance penalties" based on the position of the filter, and I suspect these don't apply to ND moon filters.

 

Just don't forget to take the ND filter off when slewing away from the moon. smile.gif

Penalties - Baader website "advice" suggests that "filter defects" are more apparent the further they are placed away from the EP. Of course their filters benefit from being HQ (so they say), so perhaps their own "advice" can be safely ignored...

 

I naively thought that the opposite would be true e.g. defect/dirt etc. that's further way from EP is more "out of focus", so matters less... of course, smaller EP filter that's "better" = "cheaper" too. Ignoring the advice, I have 2" ND to fit the diagonal for convenience with EP swaps.

 

Take the ND filter off - early days, I have bigger problems just remembering the SCT end cap always needs removing! wink.gif


Edited by SimonMiller, 03 February 2020 - 05:05 PM.

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