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27 minutes ago, Northernlight said:

Olly out of interest, can you post the full versions of those images as I would like to compare them side by side without pixel peeping 

They are a bit big but let's see what we can get away with...

First the reflector image:

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...and then the TEC 140

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The reflector used an SXVH36 (Kodak) full frame camera, the TEC an Atik 460 (Sony) with much smaller chip and smaller pixels. As mentioned earlier, the refractor image had a lot less exposure and has gone deeper but this will be more down to camera than much else. Any theorist wanting to insist that more aperture has to be faster will probably have to rely on this explanation. For those who believe in F ratio per se there is not much in it, F6.8 for the reflector, F7 for the refractor (or F7. a bit because the TEC flattener slightly extends the focal length by an amount which TEC don't disclose. It will be about 30mm.)

Hmmm, when I look through a telescope stars are round... 👹

:icon_mrgreen:lly

 

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7 hours ago, Northernlight said:

Olly, put us out of our misery, which one is which 

The spike on the large star gives it away I think

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yup but when olly posted the original images, it was cropped at center of galaxy and that very obvious star was not in the original image when i posted that comment......

 

Olly, for me the ODK image looks better, not necessarily becuase of the resolution, the ODK image just looks more natrual, but i think a lot of that might come down to processing as the Tec image looks a little overcooked on the processing side as if the curves have been pushed just a little too far as well as a tad too much sharpening on the core.

So with similar processing, i think the difference could be less pronounced between the 2 images and close the gap a bit.....

It's certainly food for thought.......Do i want a bit of extra resolution or do i want a simple life..........i think that's what it comes down too rather than comparing apertures.

 

 

Edited by Northernlight
spelling error

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14 minutes ago, Northernlight said:

yup but when olly posted the original images, it was cropped at center of galaxy and that very obvious star was not in the original image when i posted that comment......

 

Olly, for me the ODK image looks better, not necessarily becuase of the resolution, the ODK image just looks more natrual, but i think a lot of that might come down to processing as the Tec image looks a little overcooked on the processing side as if the curves have been pushed just a little too far as well as a tad too much sharpening on the core.

So with similar processing, i think the difference could be less pronounced between the 2 images and close the gap a bit.....

It's certainly food for thought.......Do i want a bit of extra resolution or do i want a simple life..........i think that's what it comes down too rather than comparing apertures.

 

 

I've nothing to argue against in any of that. If the thread has helped you in your decision then the forum's working as it should!

Olly

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Well not quite made my decision yet, but it's certainly helped, so many thanks for presenting your images. Unfortunately like most things in Astronomy the more you dig the more worms you unearth.

Whilst I know in my heart a 150mm would be the easier option, and would be very much plug and play in comparison to a newt, I'm now faced with the question : - do I want  to pay £2,000 or £4,000 for a scope.

Edited by Northernlight
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14 minutes ago, Northernlight said:

I'm now faced with the question : - do I want  to pay £2,000 or £4,000 for a scope.

Of course you do! But, naturally enough, you want to blame the rest of us. That's what we all do. I never wanted to buy a TEC140 but SGL made me do it, bless 'em! It's a self-help community... We all aim to please.

:icon_mrgreen:lly

 

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So Olly can I also send my wife in your direction when she finds out that I spent a small fortune.......Olly made me do it.

My wife's pending rage aside, I genuinely can't decide between a 150mm apo and a 10" newt 

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The dust lanes look better in the refractor image--no question--they are almost completely missing in the 14" image--I submit that the 14" is better resolved--but the refractor has more detail (count the dust lanes)--The original crops I refer to.

Rodd

Edited by Rodd

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I see the dust lanes just fine in the ODK image, though will concede the TEC has more contrast. I do not know if that is intrinsic (I suspect it is, Apos are known for their contrast) or due to processing.

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2 hours ago, DaveS said:

I see the dust lanes just fine in the ODK image, though will concede the TEC has more contrast. I do not know if that is intrinsic (I suspect it is, Apos are known for their contrast) or due to processing.

It is due to processing alone. Optics characteristics don't play a part in this level of contrast in images.

There are two types of contrast for which refractors can have edge over mirrored system of same aperture and light gathering power. Neither of them has impact on DSO imaging such that would manifest in contrast in the image.

First one is fairly simple to understand and it can be noticed when observing night sky around bright stars - its light scatter type of contrast. Mirror systems need to be very smooth in order not to produce this effect - it's often said for high quality smooth mirrors (we are not talking about figure here, but rather micro smoothness) that they have "refractor like" image. Mirror reflect most of the light as they are designed to, but some small portion of the light gets reflected all over the place. This makes sky around very bright stars look slightly washed out comparing to refractor view - sky is darker in refractor because of this (on same magnification). This is low power effect.

Other effect where it is said that refractors have more contrast is very high magnification thing - it relates to MTF of aperture and here central obstruction plays a part - it's about resolving planetary detail for example. Refractor of same aperture will provide more contrasty image of tiniest features resolved on plants, because it's unobstructed scope. Again this holds for scopes of same aperture. 8" Newtonian will have higher contrast on same scale features over 5" refractor for example (and show smaller features than 5" is able to do - it has higher resolving power).

Contrast in image above is only due to processing and SNR. Resolution is to coarse for MTF type contrast to have impact, as resolution of both images is dominated by seeing / guiding rather than aperture alone (aperture adds small difference observed, but this is still no planetary level of detail in images). Other type of contrast act just like slightly higher LP levels - it impacts SNR, but with enough exposure you can easily overcome that.

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Thanks for clarifying that Vlaiv.

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Sod it, I'm up for a challenge, 10" F5 newt with quartz mirror @ half the price and double the trouble 

Edited by Northernlight
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This is very closely related to my thread from a few weeks back, trying to work out where my FWHM values were coming from especially because I am suspicious of the mirror in my 150p.

It definitely appears as though less aperture can keep up with more in all but the best conditions we get here?

Having said that, the required fettling of the newt gives you something to do on the 350+ nights of cloud each year...

 

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