16 replies to this topic

[GeezerGazer]

I purchased an 8" Explorer Scientific CF tube f:4 Newt for NV observing and phonetography and had it out Thursday night for 3 hours during a break in cloud systems.  Humidity was above average, but transparency was pretty good otherwise and I was at my green zone for a nice dark sky.  I wanted to see how this scope would perform with my ASA .73x reducer and how images would stack up against my TEC 140.  At f:4, the Newt is working at an 800mm FL and at f:2.8 using the reducer, it is 584mm.  So if I also use a 1.5x or 2x barlow, I can get to a 1600mm FL and still be at f:8 for planetary nebulae and galaxies.  

 

My phone is an iPhone XR with 12mp sensor and with NightCap, I can now raise the ISO to 10,000 if necessary.  I don't like doing that because the grainy appearance really intrudes on the image.  But the 8" scope is as big as I'm going to go, so the availability of extra ISO may be of some help... I'll include an image with an ISO of 10000 for comparison.  

 

M42 has caused some consternation for imaging with NV, so I tried something different with it and found that if I eliminate any filters from the optical system, the image is improved.  I think this is because the function of the filters dims everything except the H-a subject and the brightest part of M42 is the core near the Trapezium which typically blows out in the image.  So below are three images for comparison; no post processing was done except for cropping for the square image and compressing by 50% to fit here.  

 

This first image is using the ES at f:4 without a filter, but with an AstroTech flattener.  The flattener helped with curvature but didn't eliminate it... stars at the perimeter are small eggs.  This image was taken at ISO 640 for 1/20s exposure averaged for 10s.  Although the extent and detail of the nebula is limited compared to a filtered image, the core/Trapezium is not so over exposed.  

 

The second image is the ES at f:4 with a 7nm H-a filter and the AT flattener; ISO 1250 for 1/4s averaged for 10s.  In this photo, the core is over exposed which is true with all of my previous efforts using an H-a filter with NV.  

 

This third image was taken through my TEC 140 using a .8x reducer and no filter.  I usually try to keep the ISO as low as possible so I took this image at ISO 125, but used a slower exposure speed at 1/4s averaged for 10s.  This arrangement also blew out the core.  Next time I use the TEC for an image of M42, I will up the ISO and shorten the exposure but lengthen the averaging time, like in the first image.

 

So for M42, not using a H-a filter helped and the standby rule of keeping the ISO low, does not necessarily apply.  A higher ISO and shorter exposure of 1/15s to 1/20s with averaging works better to avoid over exposing the core.  Next time I'm imaging I'm going to try this with a filter!  

 

Here's another comparison that reveals subtle differences.  The next image was taken with a ES 8" at f:4, ISO 4000, 1/4s for 10s

 

This image of the Horsehead, using the TEC 140 with a .8x reducer and 7nm H-a filter, ISO 5000, 1/3s for 10s, expanding this image reveals a more grainy appearance than the image above.  I won't know how these images will compare here because of the severe compression, but in the originals that have a file size that is roughly 10x bigger, the image taken through the TEC at the higher ISO and slower exposure does show a more grainy appearance.  

 

  

[GeezerGazer]

Here are two more images, the first is taken with the ES 8" with ASA reducer at f:2.8 and 7nm H-a, ISO
4000, 1/2s for 10s of the Rosette.  It's a little over exposed, but it is so vibrant with detail, I decided to include it here.

 

And the Jellyfish, taken using the TEC 140 w/7nm H-a, ISO 6400, 1/2s for 10s. 

 

Tomorrow, I'm disassembling the ES 8" to clean the mirror which arrived with a haze on the surface.  Then I'm going to reassemble, making some modifications, because on Thursday, I had to re-collimate 3 times in 3 hours!  The first ES 8" that arrived had a couple of major issues; I called ES and they promptly sent a return label.  This second scope arrived 5 days later, but had obviously been shipped out and returned to them... I think I know why.  I have been favorably impressed with the ES customer service, but the factory QC leaves me wondering.  

[GeezerGazer]

So here are a couple of very high ISO images.  The first is the Fishhead taken with the TEC 140 using a 2x barlow (at f:14) and 12nm H-a filter, ISO 8000, 1/2s for 10s

 

The Owl nebula, taken with the TEC 140 using a 2x barlow and 12nm H-a filter, ISO 10000, 1/2s for 10s

and it's still pretty dim.  The barlow raising the focal ratio to f:14, combined with the H-a filter blocking so much light, kill the image.  The scale is pretty good, but the image is so dim that it is virtually useless.  The ES 8" would have been a better choice for this subject.  

 

I have found, however, that extending the NightCap averaging time of high ISO images does help to eliminate the grainy effect.  If I had doubled the averaging time on the Fishhead, it might have been a better image.  

[Eddgie]

Some really beautiful pictures.  The Rosette Nebula shows a great amount of detail for an 8" scope!  And the field is very well illuminated all the way across with really sharp stars all the way to the edge.  Very nice.  The ASA corrector really does work well.

 

Both pics of the Horse Head and Flame are excellent.   

 

Mighty nice!

[starzonesteve]

Those images are inspiring. I’m heading out to my dark site tonight and plan on pulling out the NV with my new 20” reflector. If the images look anywhere near as good to my eye as your phone captures look I will be ecstatic.

 

Steve

[GeezerGazer]

Steve, there's always a deception when looking at photos for comparison to the visual image.  Even a 1/4 second image can far exceed the light capturing ability of our eyes.  Our eyes have better dynamic range, but the exposure time involved in photography is something our eyes cannot do.  The better comparison for your visual NV experience is between what glass eyepieces show and what your NVD reveals... which is a remarkable difference.  I use photos in place of notes and I often compare my images to long exposure AP to see how they stack up and how much detail they actually contain.  I almost never see as much detail visually as is shown in my images.  

[GeezerGazer]

Some really beautiful pictures.  The Rosette Nebula shows a great amount of detail for an 8" scope!  And the field is very well illuminated all the way across with really sharp stars all the way to the edge.  Very nice.  The ASA corrector really does work well.

I agree.  While expanding the FoV, the ASA reducer brightens and flattens the image.  Visually I see a good deal of difference between f:4 and f:2.8 in this 8" Newt.  I'm not yet convinced about the potential use of this particular 8" Newt though.  There are some niggles I have with the scope.  I'll look at it today and decide if it's a keeper.  Of course, another storm is arriving so it might take me longer than a day to make the determination.  

Edited by GeezerGazer, 27 January 2019 - 12:23 PM.

[DMala]

(...)  I'm not yet convinced about the potential use of this particular 8" Newt though.  There are some niggles I have with the scope.  I'll look at it today and decide if it's a keeper. (...)

Great pictures and info. I am surprised for the QC and collimation problems you had with the ES 8" f4 Newtonian, reading online and with no personal experience I had the impression that at that size and speed the average quality out of the box of these mass-produced Newtonians  was quite good. I like to use old scopes and I have just finished the restoration of a rather massive Edmund 8" F5 Newtonian, I am really curious to see how I will do with it, with night vision and light polluted skies. Your images are encouraging.

I am only now beginning to train my eye to detect coma, and unless mistaken I do see some of it in the ES newtonian images at F4, much less in the one Rosette Nebula example at f2.8, which overall still looks great. But I am not sure if any image was cropped to fit the thread.

[Eddgie]

The ASA reducer he is using in the 8" to get to f/2.8 corrects for coma so that is why he can go fast and have a pretty sharp field to the edge.

[Doug Culbertson]

Wow, Ray, those are stunning images. I’ve never been able to even come close to that using an iPhone and NV. 

[GeezerGazer]

I am surprised for the QC and collimation problems you had with the ES 8" f4 Newtonian, reading online and with no personal experience I had the impression that at that size and speed the average quality out of the box of these mass-produced Newtonians  was quite good. 

 

I am only now beginning to train my eye to detect coma, and unless mistaken I do see some of it in the ES newtonian images at F4, much less in the one Rosette Nebula example at f2.8, which overall still looks great. But I am not sure if any image was cropped to fit the thread.

Yes, some coma is there with the ES.  At it's native f:4, I added an AstroTech Flattener with proper spacing between it and the NVD sensor and it does help.  And on Thursday, there was a gentle wind at times; I noticed some of my images had elongated stars across the entire field!  I'm pretty sure this was from the scope catching the wind and moving during the exposure because all of the stars were elongated in the same direction.  But curvature is still visible in the egg shaped stars at the perimeter of many of my images.  Perhaps the more expensive MPCC might be the solution.  The ASA reducer/corrector (flattener) performs quite well but I also see minor curvature at the edge of some images.  Thankfully, it is below my threshold of tolerance for such aberrations!  

 

These images are really for me to see "more" than my aging eyes can see at the eyepiece visually and they are SOooo much more fun to review than my written notes!     Thursday night, when I took these images, I was really just testing to see if this scope can perform as I intended and I think it does.  I took 56 images using two different filters, the flattener, the ASA reducer and then compared them to images of the same 6 targets that I took through my TEC 140.  I found the versatility of the 8" f:4 Newt to be substantially better than the TEC because using it in prime with the reducer and barlow means that it can perform from 584mm at f:2.8 all the way to 1600mm at f:8... 1016mm of focal length variation.  That's important for scale when going from medium sized nebula to galaxies.  And I find f:8 is still OK for images with the ES 8".  The TEC has a smaller range because it begins with an f:7 focal ratio, and as a refractor, it seems harder to reduce in prime mode with satisfactory results.  I have used a .8x reducer with it and I get OK (but not great) results using a 1.5x barlow with it.  I also tried the TEC afocally using a 40mm and 55mm Plossl, but that combination resulted in curvature that was beyond my threshold.  Gavster and PeterW have used a 41 Panoptic afocally with improved results in both refractors and reflectors, so that is an option that I might explore if need be. 

 

I made a determination today, that this ES scope will be returned.  It has issues that will require some special tools that I do not have.  This was the second example of the N208CF scope that has been delivered to me in the last two weeks, directly from ES in Arizona; both have had issues.  Thankfully their customer service seems to be quite good.  It's just very frustrating.  I think the scope has excellent potential if I can just get an example that meets their advertising claims and does not have issues that are beyond my shop skills.   

[Gavster]

 

 

These images are really for me to see "more" than my aging eyes can see at the eyepiece visually and they are SOooo much more fun to review than my written notes!     Thursday night, when I took these images, I was really just testing to see if this scope can perform as I intended and I think it does.  I took 56 images using two different filters, the flattener, the ASA reducer and then compared them to images of the same 6 targets that I took through my TEC 140.  I found the versatility of the 8" f:4 Newt to be substantially better than the TEC because using it in prime with the reducer and barlow means that it can perform from 584mm at f:2.8 all the way to 1600mm at f:8... 1016mm of focal length variation.  That's important for scale when going from medium sized nebula to galaxies.  And I find f:8 is still OK for images with the ES 8".  The TEC has a smaller range because it begins with an f:7 focal ratio, and as a refractor, it seems harder to reduce in prime mode with satisfactory results.  I have used a .8x reducer with it and I get OK (but not great) results using a 1.5x barlow with it.  I also tried the TEC afocally using a 40mm and 55mm Plossl, but that combination resulted in curvature that was beyond my threshold.  Gavster and PeterW have used a 41 Panoptic afocally with improved results in both refractors and reflectors, so that is an option that I might explore if need be. 

 

Ray, when I use the 55 and 40mm plossl with my scopes, it’s not curvature thats the problem but rather edge of field aberrations where the plossl is struggling due to the fast scope speed. The 41mm pan copes with faster setups better but it is a little heavy! But with my Tec 160 at f7 I find the 55mm plossl is fine at the edge.

 

Id be very interested to see images of the 55mm plossl with your Tec 140 to see what you are getting at the edge of field?  

[starzonesteve]

Steve, there's always a deception when looking at photos for comparison to the visual image.  Even a 1/4 second image can far exceed the light capturing ability of our eyes.  Our eyes have better dynamic range, but the exposure time involved in photography is something our eyes cannot do.  The better comparison for your visual NV experience is between what glass eyepieces show and what your NVD reveals... which is a remarkable difference.  I use photos in place of notes and I often compare my images to long exposure AP to see how they stack up and how much detail they actually contain.  I almost never see as much detail visually as is shown in my images.  

What you say is true. I saw the horsehead nebula live for the first time last night using my PSV-7 attached to a 21mm Ethos using the 20". It was great to see it in real time - it was crystal clear, but did not hold a candle to the image you captured.

[Jeff Morgan]

What you say is true. I saw the horsehead nebula live for the first time last night using my PSV-7 attached to a 21mm Ethos using the 20". It was great to see it in real time - it was crystal clear, but did not hold a candle to the image you captured.

 

One thing I noticed about that image - our eyes naturally go to B33 (the HH) first.

 

Look at the emission nebula instead. Many (most?) photos show the background nebula as a fairly uniform glow - but it's not. There is a lot of subtle detail in that nebula, and Ray's cell phone image is starting to pick that up. Amazing!

[GeezerGazer]

Ray, when I use the 55 and 40mm plossl with my scopes, it’s not curvature thats the problem but rather edge of field aberrations where the plossl is struggling due to the fast scope speed. The 41mm pan copes with faster setups better but it is a little heavy! But with my Tec 160 at f7 I find the 55mm plossl is fine at the edge.

 

Id be very interested to see images of the 55mm plossl with your Tec 140 to see what you are getting at the edge of field?  

Gavin, I deleted my afocal images using the 55 Plossl last year, and I subsequently sold the eyepiece.  But if you go back to your Extreme Focal Reduction thread

 https://www.cloudyni...eduction/page-2

and look at and past post 34 on page 2, you will see results of my afocal testing using the 55... there were a few later in the thread using my TEC 140 with a 2" diagonal (the first ones were with a T2 diagonal). My recollection is that aberrations included both curvature and astigmatism.  I reviewed that thread not long ago and saw your afocal image of the HH using your 160 with 55 Plossl with ZERO aberrations at the perimeter.  An example of different optical systems providing different results I guess.  Your excellent afocal results are the reason I tried that route.  

 

I also figured out that for many of my older images, I did not have the phone bracket perfectly perpendicular to the NVD ocular, which often caused vignetting or curvature on only one side of the image.  I changed how I apply my bracket late last summer which almost completely solved that issue.  Every once in a while, the bracket gets tilted a little... it does not take much to cause a problem in the image.  

 

We have learned a lot in the last year about NV Phonetography but I still feel like I'm learning, especially because I've changed equipment several times, with manual to tracking mounts, upgraded phone with better sensor, camera lenses and going to Newts instead of refractors, and using different filters.  Yep, still learning. 

[moshen]

Wow! Just amazing image scale and detail here. Nice job! Pretty cool you can get all that in a photo so easily.

Too bad about the ES Newt, hope you can manage to get a good one.

[Jim4321]

Outstanding pix, GG!  I'm still amazed by the strong background glow around the Trapezium as seen thru the Mod 3 with a narrowband H-a filter!  It's sort of like headlights in the fog, but even that doesn't do it justice.   You captured that nicely.  The HH shots are super!

 

Jim H.