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#76 Nicole Sharp

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Posted 27 November 2018 - 04:32 AM

And as my final bit of advise...  just get the SCT prime focus adapter if you want to use a DSLR camera.  It's solid and doesn't flex.

 

Why would you WANT to use a 5X barlow with a crop sensor camera on a C5?

 

A C5 has about a 1 second of resolution.

 

The 22mm wide sensor gives you a degree-wide field.  Divide that by 6000 (roughly the number of horizontal pixels for a 24MP camera) and your pixels are already smaller than the smallest detail the scope show.  

 

You make a good point about oversampling though.  I think it could be smart to wait and see what the results look like without a Barlow before investing in them.  But then I won't be able to magnify the 24-mm reticle, so they will still work out for visual use so I don't need to buy extra eyepieces.  A 5X Barlow would be too much magnification with a 25-mm or 24-mm eyepiece, but 3X should work I think.


Edited by Nicole Sharp, 27 November 2018 - 04:33 AM.


#77 jallbery

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Posted 27 November 2018 - 09:43 AM

 I think it might just weigh less perhaps.

 

No. No. No. No. No. No. No.

 

 

If the weight advantage is the reason, you have the wrong mount.  There are a bunch of reasons...

  1. The SCT adapter gives you a 40mm-ish light path instead of a 27mm-ish one (although this is not much of an issue for a canon crop sensor).
  2. Instead of friction fit couplings, everything is threaded tight with the SCT adapter.  This reduces the possibility of flexure which can cause the camera's sensor to be slightly tilted with respect to the telescope's focal plane, causing one side of the image to be less precisely focused than the other.
  3. Because everything is threaded tight, you substantially reduce the possibility of an accident that causes the camera to crash to the ground.  (And using a barlow just increases the chance of a problem here, and also with #2.)
  4. When using the diagonal and adapter, you are positioning the additional weight very asymmetrically in reference to your main optical axis, creating balance issues.
  5. Removing the diagonal gets rid of an unnecessary optical component that can only degrade the image.
  6. When used with an appropriate T-ring, the SCT adapter will place the image plane very close to place where the scope has optimal correction of spherical aberration.  Using a diagonal and generic 1.25" adapter will require the primary to be pushed closer to the secondary, which will lead to an increase of focal length, an over-correction of spherical aberration,  and in extreme cases, a reduction of effective aperture and decrease in contrast.
  7. The standard adapter with an appropriate t-ring also will give you the proper working distance for using the F/6.3 reducer/corrector.   Using a diagonal and 1.25" adapter will increase the working distance, leading to an increase in reduction factor, and less than optimal performance.
  8. You'll no longer have mirror-image images (the image will be upside down, but that's the way the camera expects things to be).
  9. The typical 1.25" diagonal wasn't designed to hold a bulky 1-pound (or more) object (because 1.25" eyepieces don't typically weigh that much).

 

That's just what I can think of off the top of my head.

 

You are talking about a relatively light camera (compared to a DSLR, or particularly a full-frame DSLR), so that somewhat mitigates some of the above issues.  And there may be times when the diagonal solution may give you better clearance for objects near the zenith.   On the other hand, alt-az mounts don't track well through the zenith, anyway.

 

As far as the eyepiece kits (both Celestron and Meade), they come with plossls.  Plossls are a scaled design.  Eye relief is roughly 2/3 focal length.  If you want to observe with glasses, you need to spend a lot more (at least for any plossl shorter than 25-26mm).  Also note that there is often a considerable difference between published eye relief and accessible eye relief (I believe eye relief is technically measured from the middle of the eye lens element; at any rate, recessed or concave eye lenses will eat up some of the accessible eye relief) .   I have eyepieces with more than 20mm of eye relief that are not glasses-friendly.   I have a couple eyepieces with less than 20mm of eye relief that are.

 

Some people can observe with glasses using the Celestron xCel / Meade HD-60 / Starguider Dual ED / Paradigm Dual ED eyepieces that have fairly consistent eye relief across the line.   I can't (although I do like the HD-60s, but they are more comfortable to use with glasses off).  Under 20mm, my eye-glass friendly eyepieces are Baader Hyperions and Vixen LVs (I think the older design offers more accessible eye relief than the current SLV).  The other 20mm lines I'm familiar with are really expensive.


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#78 Nicole Sharp

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Posted 27 November 2018 - 12:09 PM

I've seen several posts here and on other forums about the dangers of getting too many accessories before you even have a telescope to use them with.  I'm starting to agree.  I think I'll just stick with the cases, dew shield, dew heater, power supply, and Solar filter, and then wait a month to see if I really need a DSLR, reticle, Barlows, SkySync, or StarSense for the January 2019 total Lunar eclipse.  I will try to video the ISS Solar transit in December afocally, and see how that works out.  I already have a 9-mm kit eyepiece, so I should see how that looks first with the SCT before getting anything better for planetary observing.

 

I did hear back from AstroZap about the focusing mask, and it is NOT safe to use over a Solar film filter.  Focusing has to be done the old-fashioned way, by squinting at the limb of the disc.


Edited by Nicole Sharp, 27 November 2018 - 12:12 PM.

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#79 gfstallin

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Posted 27 November 2018 - 12:42 PM

Do I need to get a dew heater in winter?  Or can I wait until it gets warmer for that?

You'll need one in the winter as well. Your part of Maryland is a little colder than mine, but I still get pretty dew-ed up during the winter months as well. It depends on the weather. 

 

George



#80 Starman27

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Posted 27 November 2018 - 11:02 PM

Nicole,

 

The M5 supports a hand held wired remote.



#81 Nicole Sharp

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Posted 28 November 2018 - 04:15 PM

Any opinions on the AstroZap vs. Baader Solar film filters for the Celestron Nexstar 5SE?

 

https://www.astrozap...r-solar-filter/

 

https://www.highpoin...filter-astf120/

 

Which might be a more secure fit?  Does it not matter?

 

My main concern is the dovetail bar, which appears to be pretty close to the edge of the OTA.  The AstroZap 6SE filter has a notch to accommodate the dovetail bar, but the 5SE version does not.

 

Outside diameter of the 5SE tube should be 152 mm.

 

https://cdn.shopify...._570x380@2x.jpg

 

https://cdn.shopify....rge_320x289.jpg

 

https://www.highpoin.../s/astf_1_1.jpg


Edited by Nicole Sharp, 28 November 2018 - 04:20 PM.


#82 Nicole Sharp

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Posted 28 November 2018 - 04:25 PM

Found this as well, which appears to be discontinued but is a lot thinner than the AstroZap version:

 

https://www.bhphotov...er_for_the.html



#83 jallbery

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Posted 28 November 2018 - 04:37 PM

You can make your own notched version...

 

A piece of Baader film big enough for a 5" scope costs about $20.

 

Here's an approach to making a filter:

https://www.ozscopes...-For-Telescopes

 

Rather than relying on a friction fit, for safety, I often use a couple pieces of painters' tape to make sure the filter stays put.


Edited by jallbery, 28 November 2018 - 04:39 PM.


#84 Nicole Sharp

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Posted 28 November 2018 - 04:39 PM

You can make your own notched version...

 

A piece of Baader film costs big enough for a 5" scope costs about $20.

 

Here's an approach to making a filter:

https://www.ozscopes...-For-Telescopes

 

Rather than relying on a friction fit, for safety, I often use a couple pieces of painters' tape to make sure the filter stays put.

 

I do not want to make my own filter.  I need something that is safe, sturdy, and reusable.



#85 jallbery

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Posted 29 November 2018 - 03:14 AM

I do not want to make my own filter.  I need something that is safe, sturdy, and reusable.

If you aren't capable of making your own in a manner that makes it safe, then you shouldn't make one.  

 

As far as sturdy, the most fragile (and critical) element is the film, which is exactly the same regardless of if you buy the $20 piece and mount it yourself, or buy the $90 model.  $70 strikes me as a lot of money for  a c5 slip on corrector cover with a 5" hole in it.   

I would certainly have no more confidence in the $90 model than one I'd make.  And of course it would be reusable.   

 

There are commercial solar filters that are nothing more than a piece of solar film mounted in a cardboard cap.

 

And just to be clear,  the tape suggestion was what I do even with a commercial filter. Particularly if other people are around...



#86 Nicole Sharp

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Posted 29 November 2018 - 03:56 AM

If you aren't capable of making your own in a manner that makes it safe, then you shouldn't make one.  

 

As far as sturdy, the most fragile (and critical) element is the film, which is exactly the same regardless of if you buy the $20 piece and mount it yourself, or buy the $90 model.  $70 strikes me as a lot of money for  a c5 slip on corrector cover with a 5" hole in it.   

I would certainly have no more confidence in the $90 model than one I'd make.  And of course it would be reusable.   

 

There are commercial solar filters that are nothing more than a piece of solar film mounted in a cardboard cap.

 

And just to be clear,  the tape suggestion was what I do even with a commercial filter. Particularly if other people are around...

I actually have an AstroZap filter for my Newtonian, and I really like it.  It is very good quality and I would say it is worth the expense compared to trying to build your own.  But on the Newtonian, it screws directly into the OTA, since there are threads available where the secondary mirror supports are.

 

I forked the Solar-filter search for the 5SE onto this thread:

 

https://www.cloudyni...on-nexstar-5se/

 

I am still waiting to hear back from Celestron and AstroZap regarding the respective dimensions to see if the AstroZap will fit onto the 5SE without the dovetail bar causing problems.  Otherwise I will probably have to get a Baader filter instead.



#87 photoracer18

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Posted 03 December 2018 - 06:05 PM

Still not sure I understand the exit pupil thing, but on paper, 32 mm looks like it works out really well with 1250 mm of focal length and a Barlow.  A 2X Barlow on a 32-mm eyepiece with a 52-degree AFOV provides a TFOV of 1.2 Lunar diameters, which is the exact same true field of view I would get on a Canon APS-C sensor at prime focus.  So the 32-mm eyepiece basically works as a DSLR simulator, so I can go back and forth between visual observing and prime-focus imaging always seeing the same true field of view (with the 2X Barlow).

Sorry, but I just entered you info into CCD Calculator and a C5 + 2x Barlow + Canon APS-C DSLR will clip the top and bottom of the Moon off the camera's FOV. When calculating how an object fits in the camera's FOV you only use the smallest dimension of the sensor, in this case 14.8mm.

Moon.JPG

 

This is the Canon DSLR FOV without the Barlow:

 

Moon-1.JPG

 

An Antares 1.6x 2" Barlow may work better and get the entire Moon in without clipping. Nope that won't fit either.


Edited by photoracer18, 03 December 2018 - 06:18 PM.


#88 photoracer18

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Posted 03 December 2018 - 06:34 PM

This is what your eye will see with a 32mm Plossl and the C5 with and without the 2x Barlow. The only camera that can capture the entire Moon with a 2x Barlow and the C5 is a full frame DSLR like a Canon Eos 5D or something similar.

Here is the camera FOV of a Canon EOS 5D + 2x Barlow + the C5.
Moon3.JPG

#89 Nicole Sharp

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Posted 03 December 2018 - 06:35 PM

Sorry, but I just entered you info into CCD Calculator and a C5 + 2x Barlow + Canon APS-C DSLR will clip the top and bottom of the Moon off the camera's FOV. When calculating how an object fits in the camera's FOV you only use the smallest dimension of the sensor, in this case 14.8mm.

attachicon.gif Moon.JPG

 

This is the Canon DSLR FOV without the Barlow:

 

attachicon.gif Moon-1.JPG

 

An Antares 1.6x 2" Barlow may work better and get the entire Moon in without clipping. Nope that won't fit either.

I actually canceled the order for the 5SE:

 

https://www.cloudyni...ronomy-with-c5/

 

A C5 will have a margin of only 0.01 Lunar diameters on a Canon APS-C sensor recording in 1080p.

 

It would have a margin of 0.1 Lunar diameters though if taken using continuous shooting and then time-lapsed.

 

I think a small refractor and a 2X Barlow would work out better (and more cheaply) for full-disc Solar/Lunar imaging.


Edited by Nicole Sharp, 03 December 2018 - 06:36 PM.


#90 jallbery

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Posted 04 December 2018 - 10:04 AM

This is what your eye will see with a 32mm Plossl and the C5 with and without the 2x Barlow. The only camera that can capture the entire Moon with a 2x Barlow and the C5 is a full frame DSLR like a Canon Eos 5D or something similar.

Here is the camera FOV of a Canon EOS 5D + 2x Barlow + the C5.
attachicon.gif Moon3.JPG

Then why use a 2X barlow? 

 

 

I actually canceled the order for the 5SE:

 

https://www.cloudyni...ronomy-with-c5/

 

A C5 will have a margin of only 0.01 Lunar diameters on a Canon APS-C sensor recording in 1080p.

 

It would have a margin of 0.1 Lunar diameters though if taken using continuous shooting and then time-lapsed.

 

I think a small refractor and a 2X Barlow would work out better (and more cheaply) for full-disc Solar/Lunar imaging.

 

Not sure I get your math...

 

A Canon APS-C sensor is 14.8mm tall

 

14.8*57.3/1250 =  0.67 degrees or just under 41 arc minutes (40.709).

 

The moon is roughly 31 arc minutes in angular size.  41-31 = 10  10/ 2 = 5.   5/31 = about 0.16 lunar diameters of separation on both top and bottom.

 

Shooting in a 16:9 mode will reduce the height of the frame by a 0.85X, I believe (3368 pixels of the 4000 vertical pixels in the sensor).  This yields a 34.6 arc minute height, which is definitely tight.  But even here we have 40.7 - 34.6 = 6.1    6.1/2 = 3.05   3.05/31 = about 0.05 lunar diameters. 

 

Even with a 32 arc minute disk, I still get 0.045 lunar diameters, which is very tight, but not as tight 0.01...

 

Put on the F/6.3 reducer and you'll have plenty of breathing room.  (0.5 lunar diameters, or 0.35 lunar diameters)

 

If that makes the moon too small for your tastes, you could use less than 100-105mm of spacing between the reducer and the sensor, and  increase the size of the disc in the frame.   

 

I question that a refractor solution would be cheaper AND better...   You could get cheaper.  You could get better.  But I doubt you will find both.

 

An 80mm F/5 achromat would mean a cheaper OTA.  But it will suffer from a lot of CA and have less resolution, so I don't see it as being better.   And when you stick on a 2X barlow, you'll be at 800mm (possibly a bit more).

 

A 90mm F/11.1 achromat is cheap, and address much of the SA issues, but it's still not going to match the C5 for resolution, and its going to require a much more substantial mount for good results.

 

An 80mm ED doublet might compete in detail with the C5, but even the most affordable ones plus a suitable mount will cost more than a 5SE.  And at F/7.5 (the typical focal ratio for the more affordable 80EDs), you get a 600mm focal length (too short), or 1200mm with a 2X barlow (rather close to the C5).  Using a 2X barlow with a camera will probably give you more than a 2X boost, so you could end up worse off than you were with the C5.

 

A faster ED doublet than an F7.5 80ED, plus a 2X barlow could give you the focal length you desire, but it will cost substantially more than a C5.




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