alex_stars

8 hours ago, Nik271 said:

34% is basically the same as a C8 SCT, that's disappointing.

I agree, that is indeed disappointing, given that I got my Mak to have better contrast than a SCT. 😞 Well well, it's still a nice scope...

@Nik271, great work.

My weather conditions did not allow yet for some nighttime testing, but I took this photo just now on my desk.

Its basically a zoomed smartphone image into the EP-holder (no diagonal) and the scope against a white wall. You can see the smartphone lens reflection in the secondary. Also when you look at the supposedly black areas outside the primary, you see that my baffle tube could do with some flocking  

Anyhow if I measure the central obstruction here, I get 34%. So there we go.

@Nik271 great image of Polaris BTW 👍

1 hour ago, Nik271 said:

It's probably a bit better than that because the front meniscus is a negative lens, i.e. the 180mm front aperture gets 'dispersed' into wider beam, I presume between 190 and 200mm which is captured by the primary. This image is than reflected by the secondary into the rear opening, so the size of the image of the central obstruction will change in the final image circle.

Right. However I was wondering what aperture vs obstruction values actually define the resolution of the telescope. Is it

• the 37/180 = 20% at the meniscus lens?
• or is it 63/180 = 35% (taking the primary mirror hole and the front aperture)?
• or is it 63/190 = 33% (taking the primary mirror hole and the dispersed beam)?

I don't know the answer on top of my head. Probably should research that, or measure the modulation transfer function (MTF) at one point, that would describe the whole system.

@Captain Magenta, thanks for the details.

Cheers,

Alex

22 hours ago, Nik271 said:

Incidentally I realised the effective central obstruction is not 20% because it's not  coming from the secondary. In fact it's over 30%: As your very helpful measurements show it comes from the retaining ring of the primary which is 63mm. So the central obstruction linear ratio is 63/200 =31.5%. Still small but not even close to the 20% advertised.

Nikolay

Hi @Nik271,

I agree this is rather upsetting. However it gets even worse. Given that the primary mirror is oversized (200 mm instead of required 180 mm) to presumably avoid edge effects of a non-perfect mirror, we should probably calculate with 63/180, resulting in a 35 % linear central obstruction. If this is indeed the case it would be on a similar visual contrast level as the typical SCs, say a C8 (33.8 %) or a C9.25 (36.2 %). Both would have more aperture and thus more resolution, especially for imaging.

This will keep me thinking for a while now.

Clear skies,

Alex

23 hours ago, Captain Magenta said:

Basically, I've added the following: "Primary FL: 463.3mm +/- 1.6mm; Secondary FL: 115.7mm +/- 0.7mm"

Hi Magnus,

I see you have revised your primary FL (F1) also down to 463.3 from the initial 472 mm. When I run my estimates with this F1, I get a secondary FL (F2) of 114.6+/-0.7mm, so we agree within error bars. 😀. May I ask what caused the revision of the primary FL?

Clear skies,

Alex

@vlaiv Thanks! Great to see the theoretical background and very helpful info in figuring out what is possible with a given setup.

On 04/07/2019 at 11:24, vlaiv said:

Yes, exact workflow was:

- Take original image and blur it with Airy pattern of certain aperture (and I included 25% central obstruction)

- Resample each copy of original blurred image to certain sampling rate

- Apply wavelets to each copy

- Resize images to the same size for easier comparison

Hi @vlaiv,

I just have another question on your workflow. When you applied the wavelet filter to each copy, did you use the same filter for all images or did you "optimize" for each sampling resolution? In case you applied the same wavlet filter setting for all resolutions, did you optimize that one on the highest sampling (x6pp)?

Thanks @vlaiv for the explanation. At my current setup (180 Mak and a ASI224 MC), I can get about 0.3"/px without a barlow and 0.15"/px with my barlow. So that should be just optimal sampling.

Now I can experiment with the processing and try your suggested processing path for very sharp results. I also prefer sharp images instead of large one.

Clear Skies!

Hi @vlaiv,

I really like your analysis and examples. I just started thinking about this, so here is a question:

In the above post you recommend double the sampling rate for a colour camera than for a mono camera. Is this related to the Bayer filter these cameras use? Can you maybe explain the argument for double the sampling rate.

Clear Skies

Thanks for sharing the capturing and processing details @GuLinux, as said, makes comparing a lot easier. 😉

Just for reference for those who are into numbers, the sampling scale would be around 0.18 arcsec/pixel. I like to compare that number. In my case I need to barlow for that sampling as my ASI224 MC has a lot larger pixels (3.75 µm in comparison to your 2.4 µm).

Clear Skies.

Fantastic image with a C6. I agree, really inspiring! 

I agree with @Tommohawk. Its great to see wonderful results of scopes in the 7-8" range as these are more "accessible" to most of us. Not everyone can go and grab a C14. Very well done @GuLinux. Lot's of detail!

@GuLinux, would you share your effective focal length of that photo or the sampling scale. That would be great for further comparisons.

Very nice!

Thanks @michael.h.f.wilkinson! Good to know the setup sometimes to compare and see what would be possible. That would make a sampling scale of 0.2 arcsec/pixel on your setup if I did the math right.

I will make an attempt tonight with my 180 Mak. Let's see if the sky remains clear.

Clear Skies,

Fantastic animation. I am so amazed to see Olympus Mons rotating. May I ask which scope you used?

Thanks @Nik271 for the nice report. Great reminder to have the Pup on the radar of things to observe.

The other day I was imaging Mars and used Mesarthim (Gamma Ari and Gamma 1 Ari) to focus my Mak and I had no problems resolving the two. They are 7.5" apart. Sirius B should be 11.2" away from Sirius A so I think it really is the time to hunt for the Pup.

Looking forward to read more reports during the season.

Clear Skies.

Lots of great surface features visible. Love how the clouds pop up in the composite. 👍 Must have been really good seeing conditions. I wait for those at my location.....

Fantastic first Mars image, well done👍. Really nice features visible.

Great comparison, a real difference between the years! 👍 Guess it tells us that now its the time to image Mars... before it too late 😉. 

@Yawning Angel, love the new color tuned version!! It displays the surface features and the clouds a lot better I'd say.

Clear Skies

I agree with @johnturley, given your, @M40, current setup, these single shots are remarkable indeed. Well done.

Not sure if you need the colour filters with your DSLR?

Also, when recording videos for planetary imaging, watch out that your DSLR is not compressing the video, else all your beautiful detail is gone. In the end a dedicated camera makes life a lot easier for planetary imaging. And you can get the entry level ones for not too much money.

Looking forward to see more images.

Clear Skies.

Great image @Yawning Angel 👍 Nice cloud details, the S-pole cap nicely visible and great surface structure. A slight bit bias towards the blue maybe?

1 minute ago, astroman001 said:

Well done, a 3x or 5x Powermate will help increase image scale.

Peter

Thanks Peter👍. I plan to increase the scale by using different spacers between the Hyperion Barlow and my camera. I should be able to get beyond 3x that way.

Hi @M40, nice images. Did you stack those and did you calculate their resolution? Do let us know a bit more on how you processed those, for comparison reasons.

HI @johnturley and thanks. Yes we should keep an eye on the South Polar cap. Let's see if it disappears or not.

Clear Skies!