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Deisler

After two sessions with stock 200P - eyepiece upgrade advice?

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2 hours ago, Raph-in-the-sky said:

I know its all relative and depends on one's taste but I will tell you what I would do if I were in your shoes (and I was not long ago).

So, for £200, I would get BST Starguiders 5mm and 15mm, a GSO/Revelation 32mm Plossl and instead of the Barlow I would get a decent UHC filter (Explore Scientific sells for £44 at FLO).

Hi,

May I ask if the UHC filter works well in light polluted sky? My postcode has Bortle number 5.

Cheers

Deisler

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7 minutes ago, Deisler said:

Yes sir. I bought it but not yet used it. I used the stock finderscope and found it very difficult to hop between stars. I tried to follow bright stars in Andromeda to locate the galaxy but it is almost impossible for an inexperienced observer to do. I heard Telrad will help me a lot, so I certainly look forward to using it!

I am waiting for my plastic band to arrive tomorrow so I can fix it onto the tube. I don't like to apply the glue thing straight away as I fear I might do something wrong to ruin my tube. Maybe I am just being too cautious. 

Thanks

 

Good man! Telrad is the best kind of finder IMHO. Placing it first with something temporary to check if the position suits you is the correct way to do it. Afterwards you could fix it permanently.

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6 minutes ago, Deisler said:

Hi,

May I ask if the UHC filter works well in light polluted sky? My postcode has Bortle number 5.

Cheers

Deisler

Bortle 5 isn't that bad actually (I live in Bortle 9). UHC works well under a light polluted sky but will yield even better results under dark skies. My advice is to try to go to a dark place at least every once in a while ... it's worth it if you can manage

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13 hours ago, John said:

My regular eyepieces are Tele Vue and Pentax but I've owned and used a few BST Starguiders and I think they are really pretty good eyepieces for their cost (£50 new, £30 or so on the used market).

 

Have you tried the Tele Vue Plossls by any chance?

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6 minutes ago, Raph-in-the-sky said:

Bortle 5 isn't that bad actually (I live in Bortle 9). UHC works well under a light polluted sky but will yield even better results under dark skies. My advice is to try to go to a dark place at least every once in a while ... it's worth it if you can manage

I surely will!

One quick question if you don't mind - re 'BST EPs' - do you think I should get a 5mm or 8mm, in addition to 15mm EP? 5mm will give me 240x mag, which I assume is for planetary view? Would 5mm also be useful for moon view? or 8mm maybe more useful for both planetary and moon?

I probably will only buy one high-power EP at this stage. 

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2 minutes ago, Deisler said:

I surely will!

One quick question if you don't mind - re 'BST EPs' - do you think I should get a 5mm or 8mm, in addition to 15mm EP? 5mm will give me 240x mag, which I assume is for planetary view? Would 5mm also be useful for moon view? or 8mm maybe more useful for both planetary and moon?

I probably will only buy one high-power EP at this stage. 

This is a very good question. x240 is probably the maximum magnification that you would be able to use on a semi regular basis. If you go for an 8mm, you will  be able to use it more often but you won't be able to push the magnification when you have a very good night which might be frustrating. These EPs will be used mainly for the moon, the planets, globular clusters and double stars. 

If you plan to get a Barlow at some point maybe you won't need the 8mm (15mm/2=7.5mm).

Sorry for not giving you a definitive answer. I got the 5mm first but was really happy when I got an 8mm... Then I realised that 11mm would be nice too and bought a Nagler.... now contemplating buying a 30mm APM UFF.

The quests for the right set of EPs for you is long and difficult and in the end it is very likely that you end up with a 5mm and an 8mm. Deciding what you want first is a matter of "do I feel the need to be able to push my scope to its limits when the weather is right or do I want an EP that I would use more often". I know I felt the need to be able to push the scope but I'm pretty many on SGL would advise against that.

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34 minutes ago, Raph-in-the-sky said:

This is a very good question. x240 is probably the maximum magnification that you would be able to use on a semi regular basis. If you go for an 8mm, you will  be able to use it more often but you won't be able to push the magnification when you have a very good night which might be frustrating. These EPs will be used mainly for the moon, the planets, globular clusters and double stars. 

If you plan to get a Barlow at some point maybe you won't need the 8mm (15mm/2=7.5mm).

Sorry for not giving you a definitive answer. I got the 5mm first but was really happy when I got an 8mm... Then I realised that 11mm would be nice too and bought a Nagler.... now contemplating buying a 30mm APM UFF.

The quests for the right set of EPs for you is long and difficult and in the end it is very likely that you end up with a 5mm and an 8mm. Deciding what you want first is a matter of "do I feel the need to be able to push my scope to its limits when the weather is right or do I want an EP that I would use more often". I know I felt the need to be able to push the scope but I'm pretty many on SGL would advise against that.

yeah that makes perfect sense. I think I will go for 5mm EP, skipping 8mm for now. Then if I really want 8mm, I can always get a decent barlow later.

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Hi guys,

Just to summarise what I have learnt so far from great advice you guys have given me and what I decide to do for my EP upgrade -

1) will get BST StarGuider 60º 5mm/15mm ED EPs - ~£45 each

2) will get a wide field low-power EP, currently leaning towards Aero 2'' 30mm (£100), but 32mm GSO Plossl (£33) is much cheaper but with some negative comments (like distorted view). 

3) will get a filter - still need to research this topic, i.e. UHC v.s OIII;

4) Next, probably in a six months time, I will buy a TV barlow or a TV PM, depending on if I need greater eye relief on my BST EPs.

 

Re. the wide field low-power EP, can you guys comment on 'Aero 2'' 30mm vs 32mm GSO 1.25'' vs other options' for my 200P Dob? 

I quite enjoy low-power view (through my stock 25mm) and found it very relaxing - so I want to buy a good one that will always be in my EP case. Any advice?

Cheers

Deisler

Edited by Deisler

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5 minutes ago, Deisler said:

Hi guys,

Just to summarise what I have learnt so far from great advice you guys have given me and what I decide to do for my EP upgrade -

1) will get BST StarGuider 60º 5mm/15mm ED EPs - ~£45 each

2) will get a wide field low-power EP, currently leaning towards Aero 2'' 30mm (£100), but 32mm GSO Plossl (£33) is much cheaper but with some negative comments (like distorted view). 

3) will get a filter - still need to research this topic, i.e. UHC v.s OIII;

4) Next, probably in a six months time, I will buy a TV barlow or a TV PM, depending on if I need greater eye relief on my BST EPs.

 

Re. the wide field low-power EP, can you guys comment on 'Aero 2'' 30mm vs 32mm GSO 1.25'' vs other options' for my 200P Dob? 

I quite enjoy low-power view and found it very relaxing - so I want to buy a good one that will always be in my EP case. Any advice?

Cheers

Deisler

For the filter, most of us start with a UHC because you can use it on more targets. The OIII's main/most famous target is the veil nebula which is amazing and warrants the purchase of an OIII by itself (especially since it is very dificullt to see without it).

Regarding the low power EP, I'm currently having the same questioning. I am currently using a GSO 32mm plossl which I find does a decent job but only give 1.38° of true field of view so I'am considering upgrading.

So far the contenders are:

1) Skywatcher Aero 30mm +-£110

2) Skywatcher Panaview 32mm +-£100

3) APM UFF 30mm +-£180

In the end, it might just come down to what I can find in second hand.

 

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I did not find anything wrong with GSO 32mm in F/6 8" dob, but then again did not look for it either. It served me fine for a long time, I still have it although I don't use it anymore because I replaced it with 28mm 68 degree ES.

Later gives me better view because of higher magnification (makes sky darker in LP) and of course nicer 68 degree FOV vs ~50 of GSO.

I also though about getting largest possible FOV for another scope (F/10 1000mm one) so I examined all available options. My initial idea was to use x0.67 reducer with F/10 scope and 28mm EP to get maximum TFOV - but that proved rather difficult as distance needed is 85mm - small enough for 2" diagonals, larger then 1.25" (and reducer needs 2" to be able to show that much sky).

In any case - getting largest possible TFOV will require rather large field stop - around 46mm. Most eyepieces are reported soft around the edges - but that is no wonder because most scopes are not well corrected on such a large circle - most perform good up to 30mm or so - That makes me wonder if it is at all feasible to get large FOV on long focal length or if it is better to simply use another scope that has short focal length in the first place.

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The 30mm Aero ED's are better corrected at the field edges than the Panaview although they won't be perfect at F/6. They (the Aero ED's) can be found for £50 on the used market.

 

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Now that we're talking about low power 2" eyepieces, I'll add that found the 35mm Aero ED to be quite usable, but definitely not perfect.  It has nearly the maximum true field of view available in a 2" eyepiece.  I haven't tried the 30mm Aero ED because I've got the 30mm APM UFF which would be hard to improve upon.  Below are some comparison photos I took of and through my wider eyepieces to give you some idea of what to expect.

1503910180_29mm-30mm.thumb.JPG.beb0e0b0d494a0fb027e38e2a180acef.JPG1270098715_29mm-30mmAFOV.thumb.jpg.b72cf50a97eb28a4217fd5188677c85a.jpg

1633940429_32mm-42mm.thumb.JPG.bef44bf60fe3e68cfbac5e7ed8712d66.JPG2142447751_32mm-42mmAFOV.thumb.jpg.dead789621328694a186dcce97a21653.jpg

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14 minutes ago, Louis D said:

Now that we're talking about low power 2" eyepieces, I'll add that found the 35mm Aero ED to be quite usable, but definitely not perfect.  It has nearly the maximum true field of view available in a 2" eyepiece.  I haven't tried the 30mm Aero ED because I've got the 30mm APM UFF which would be hard to improve upon.  Below are some comparison photos I took of and through my wider eyepieces to give you some idea of what to expect.

 

Hi Louis,

May I ask if the distortion at left-right boundaries of the visible part of the ruler was because of the image taken by a camera, or it will look like that visually?

The Aero one does seem to have very bad distortion at boundaries.

Cheers

 

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2 hours ago, Deisler said:

Hi guys,

Just to summarise what I have learnt so far from great advice you guys have given me and what I decide to do for my EP upgrade -

1) will get BST StarGuider 60º 5mm/15mm ED EPs - ~£45 each

2) will get a wide field low-power EP, currently leaning towards Aero 2'' 30mm (£100), but 32mm GSO Plossl (£33) is much cheaper but with some negative comments (like distorted view). 

3) will get a filter - still need to research this topic, i.e. UHC v.s OIII;

4) Next, probably in a six months time, I will buy a TV barlow or a TV PM, depending on if I need greater eye relief on my BST EPs.

 

Re. the wide field low-power EP, can you guys comment on 'Aero 2'' 30mm vs 32mm GSO 1.25'' vs other options' for my 200P Dob? 

I quite enjoy low-power view (through my stock 25mm) and found it very relaxing - so I want to buy a good one that will always be in my EP case. Any advice?

Cheers

Deisler

Remember, FLO offers increasing discounts on BST Starguiders as you buy more of them.

I compared them to their Meade HD-60 equivalents in this thread and found them quite comparable despite their lower price.

In my previous post, you can compare the 32mm GSO Plossl to the 35mm Aero ED.  Even the 30mm 80 degree eyepiece (Agena UWA above) (generically available for low cost on ebay) shows at least as much well corrected field in the center as the 32mm GSO Plossl while providing a poorly corrected outer field for context.

If you live under heavily light polluted skies, I'd get a quality OIII filter because it really blocks light pollution quite well.  You give up the Hydrogen Beta line as seen below, but I've never missed it:

spacer.png

I rarely use Barlows any more despite owning 7 of them in 1.25" and 2" sizes as well as a TV PBI.  Individual eyepieces are just easier to deal with unless you leave the Barlow in the focuser all night to operate continuously at higher magnifications.

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The edge distortions will depend on the spec of the scope that the eyepiece is used in. In an F/10 or slower scope, most eyepieces are sharp to the edge of the field of view. At F/4 most will show some distortion.

Scopes also have some distortions of their own to add to the mix eg: coma with a newtonian and field curvature with refractors.

I don't know what spec of scope Louis D's field photos were emulating. It would be interesting to know :smiley:

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4 minutes ago, Deisler said:

Hi Louis,

May I ask if the distortion at left-right boundaries of the visible part of the ruler was because of the image taken by a camera, or it will look like that visually?

The Aero one does seem to have very bad distortion at boundaries.

Cheers

 

Nope, not the camera, it's the eyepiece.  Notice how sharp the 40mm Meade SWA is right almost to the edge with nearly the same apparent field of view.  You can also see that the 30mm ES-82 is fairly sharp nearly to the edge.  I tilted the camera to get the edge in sharpest focus possible to show the field stop sharpness in that little extra bit of image to the right of the main image since my camera only goes to about 75 degrees on the diagonal.  I bought a second super wide field camera to capture the entire field in one go in the "full width" images.  However, it is a lower resolution camera and I had to up-sample the images to match the image scale of the 75 degree camera, so the utility of those images isn't all that great.

There just is no free lunch when it comes to wide field and good image correction across that field.  If you want both at the same time, it means getting a big, heavy eyepiece.  Notice how nicely corrected the Baader Scopos Extreme is.  However, it's weight slots it between my 12mm and 17mm ES-92 eyepieces, which is to say very heavy.  Your best bet for well corrected and lighter weight is the 30mm APM UFF.  However, it is fairly expensive, though still cheaper than TV Panoptics.

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12 minutes ago, John said:

The edge distortions will depend on the spec of the scope that the eyepiece is used in. In an F/10 or slower scope, most eyepieces are sharp to the edge of the field of view. At F/4 most will show some distortion.

Scopes also have some distortions of their own to add to the mix eg: coma with a newtonian and field curvature with refractors.

I don't know what spec of scope Louis D's field photos were emulating. It would be interesting to know :smiley:

They were taken through my f/6 AstroTech 72mm ED with a TSFLAT2 field flattener ahead of the 2" GSO 99% dielectric diagonal spaced at 15mm with an SCT to M48 thread adapter (original diagonal nosepiece removed) with about 35 feet of separation indoors between the target and the scope's objective.  As I said above, it's clear that certain camera/eyepiece combinations will yield sharp images to the diagonal limits of the camera (a Galaxy S7 phone camera).  Check both edges for sharpness because I sometimes ended up with one or the other being slightly sharper due to camera tipping or centering issues.  There's very little residual field curvature or edge aberrations from the objective itself.  It's also unobstructed, so that's one less variable when it comes to evaluating eyepieces.  The images I captured pretty closely resemble what I saw through each eyepiece with my eyes while wearing eyeglasses to correct for my strong astigmatism.  Each eyepiece was focused for infinity corrected vision to hopefully show the field stop sharpness at its best since focusing for near or far sightedness can move the image plane ahead of or behind the field stop location causing it to look fuzzy.

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5 minutes ago, Louis D said:

Nope, not the camera, it's the eyepiece.  Notice how sharp the 40mm Meade SWA is right almost to the edge with nearly the same apparent field of view.  You can also see that the 30mm ES-82 is fairly sharp nearly to the edge.  I tilted the camera to get the edge in sharpest focus possible to show the field stop sharpness in that little extra bit of image to the right of the main image since my camera only goes to about 75 degrees on the diagonal.  I bought a second super wide field camera to capture the entire field in one go in the "full width" images.  However, it is a lower resolution camera and I had to up-sample the images to match the image scale of the 75 degree camera, so the utility of those images isn't all that great.

There just is no free lunch when it comes to wide field and good image correction across that field.  If you want both at the same time, it means getting a big, heavy eyepiece.  Notice how nicely corrected the Baader Scopos Extreme is.  However, it's weight slots it between my 12mm and 17mm ES-92 eyepieces, which is to say very heavy.  Your best bet for well corrected and lighter weight is the 30mm APM UFF.  However, it is fairly expensive, though still cheaper than TV Panoptics.

I was under impression that you were using DSLR and a lens. In case you have one - we can easily calculate focal length of lens that you would need to capture all eyepieces up to field stop. Let's take 100 degrees to be maximum AFOV currently available. If you use APS-C sized chip (most likely in consumer type DSLR) - that is about 28mm across. You would need something like 12mm lens to get it covered.

Btw - what scope did you use it with?

And what was the distance to rullers?

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Just now, vlaiv said:

I was under impression that you were using DSLR and a lens. In case you have one - we can easily calculate focal length of lens that you would need to capture all eyepieces up to field stop. Let's take 100 degrees to be maximum AFOV currently available. If you use APS-C sized chip (most likely in consumer type DSLR) - that is about 28mm across. You would need something like 12mm lens to get it covered.

Btw - what scope did you use it with?

And what was the distance to rullers?

It's not possible to use DSLR lenses for digiscoping with most eyepieces because you'll get severe vignetting due to the huge mismatch in diameters between the eyepiece eye lens and the camera lens's objective lens.  You have to use cameras with tiny lenses.  Today phone cameras are perfect for this task.  They are surprisingly well corrected and high in resolution compared to what was available in digital P&S cameras 15 to 20 years ago.

That other camera is 135 degrees on the diagonal (LG G5).  Unfortunately, it's only 5 megapixels.  It also has a weird white balance that is consistently yellowed.

You can't use eyepiece projection directly onto the sensor, either, because most eyepieces don't project a flat field.  You really need a lens on the camera to emulate the human eye's interaction with the eyepiece's exit pupil.  In my case, the depth of field of the camera lens actually makes eyepieces with field curvature look better than they do to my presbyopic eyes.

Your other two questions are answered in my earlier post I was composing when you responded.

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8 minutes ago, Louis D said:

They were taken through my f/6 AstroTech 72mm ED with a TSFLAT2 field flattener ahead of the 2" GSO 99% dielectric diagonal spaced at 15mm with an SCT to M48 thread adapter (original diagonal nosepiece removed) with about 35 feet of separation indoors between the target and the scope's objective.  As I said above, it's clear that certain camera/eyepiece combinations will yield sharp images to the diagonal limits of the camera (a Galaxy S7 phone camera).  Check both edges for sharpness because I sometimes ended up with one or the other being slightly sharper due to camera tipping or centering issues.  There's very little residual field curvature or edge aberrations from the objective itself.  It's also unobstructed, so that's one less variable when it comes to evaluating eyepieces.  The images I captured pretty closely resemble what I saw through each eyepiece with my eyes while wearing eyeglasses to correct for my strong astigmatism.  Each eyepiece was focused for infinity corrected vision to hopefully show the field stop sharpness at its best since focusing for near or far sightedness can move the image plane ahead of or behind the field stop location causing it to look fuzzy.

I don't think that distance will be much of an issue. It can only contribute to bit of spherical aberration, but with most of these eyepieces and their focal lengths it is too low impact to show on images. Field stop will be in focus - close focusing just moves focal plane further out but does not change focal plane of the eyepiece (which is ideally at field stop to make it sharp).

On the other hand - use of field flattener that has exact operating distance could be an issue for edge performance of some of the eyepieces. You did get about good spacing for it - it should be located at about 128mm away from focal plane, and GSO diagonal adds 110mm of optical path + 15mm of optical path of SCT/M48 adapter that makes about 125mm total - let's call it close enough. This would be generally ok if all eyepieces had their focal point right at the shoulder - but eyepieces vary by quite a bit and some may need up to 10mm of adjustment either way - that would make field flattener introduce significant astigmatism - which would show as EP astigmatism.

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2 minutes ago, Louis D said:

It's not possible to use DSLR lenses for digiscoping with most eyepieces because you'll get severe vignetting due to the huge mismatch in diameters between the eyepiece eye lens and the camera lens's objective lens.

Not sure why would it be so?

If you place camera lens at exit pupil - all light from EP will certainly hit camera lens without any issues.

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2 minutes ago, vlaiv said:

I don't think that distance will be much of an issue. It can only contribute to bit of spherical aberration, but with most of these eyepieces and their focal lengths it is too low impact to show on images. Field stop will be in focus - close focusing just moves focal plane further out but does not change focal plane of the eyepiece (which is ideally at field stop to make it sharp).

On the other hand - use of field flattener that has exact operating distance could be an issue for edge performance of some of the eyepieces. You did get about good spacing for it - it should be located at about 128mm away from focal plane, and GSO diagonal adds 110mm of optical path + 15mm of optical path of SCT/M48 adapter that makes about 125mm total - let's call it close enough. This would be generally ok if all eyepieces had their focal point right at the shoulder - but eyepieces vary by quite a bit and some may need up to 10mm of adjustment either way - that would make field flattener introduce significant astigmatism - which would show as EP astigmatism.

However, focusing out distance issues with your eye can move the image plane away from the field stop as I stated above, thus I focused wearing distance corrected eyeglasses.

I know about the shoulder issue.  I face the same issue with my GSO CC.  Luckily most of my eyepieces focus within 5mm of the shoulder.  To test your theory, check my image below of my 12mm Nagler T4 which focuses 19mm from the shoulder in two inch mode.

1920390915_12mm-12.5mmAFOV.thumb.jpg.245b384c069b3e9baab028193a468c7d.jpg

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3 minutes ago, Louis D said:

To test your theory, check my image below of my 12mm Nagler T4 which focuses 19mm from the shoulder in two inch mode.

That is not going to help much - it's a 12mm eyepiece - means that field stop is about 17.1mm - that is only about 8.6mm from axis - about a third of a distance from field center compared to edge of 46mm field. Even if you introduce large distance error for flattener - that part of the field will not be significantly distorted.

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8 minutes ago, Louis D said:

Luckily most of my eyepieces focus within 5mm of the shoulder.

In any case - I think that we can use your comparison as a good indicator of edge performance of eyepieces - all issues discussed above will probably have rather small impact at these magnifications.

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