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glassless m27

alacant

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alacant

alacant

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Hi everyone. I think this is about as 'glassless' (GL) as it gets. AFAICT, the only material denser than air through which the light has passed is whatever's left in front of the sensor. Also nice to have a decent size nebula in the frame. Thanks for looking, clear skies and of course any comments +ve or -ve most welcome. Especially along GL lines.

Bresser nt150/1200; 60 minutes

27-1.thumb.jpg.7b0d9d1120f35bff5b812a61e7a147ec.jpg

 

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Ruud

Ruud

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It's nice and bright, and rich in detail. Still, glass is used for the mirror I guess, and you need a glass to hold the champagne to make a toast on this successful image. Cheers!

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alacant

alacant

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7 hours ago, HunterHarling said:

Glassless...?

The light hasn't passed through any glass; no lenses, coma correctors, field flatteners or filters.

7 hours ago, Ruud said:

glass is used for the mirror 

But the light hasn't passed through it. And cheers BTW!

7 hours ago, HunterHarling said:

What camera

Canon 700d.

--- --- ---

Thanks everyone for your time and comments.

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Chris

Chris

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On 7/17/2017 at 10:11, alacant said:

comments +ve or -ve most welcome. Especially along GL lines.

It's a lovely image but I personally don't quite see it as glassless if there is glass in the telescopes light path, nothing personal, I didn't see it has glassless when I was using a Newt without coma corrector and all filters removed camera (does your camera have all the filters removed?) From the title I thought you'd used plastic lenses or a speculum metal mirror. It's nice and flat without a coma corrector though, did you crop the image much to flatten it?

Did you need flats? I've noticed that the Bresser has a big bore focuser which might remove the need for flats with a little cropping? 

Anyway, I like glass in scopes, I say keep glass involved :icon_biggrin:

 

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alacant

alacant

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42 minutes ago, Lockie said:

don't quite see it as glassless

Hi and thanks for your comments. My poor explanation. I meant light passing through glass. I find that every time I add glass to the light path, the stars and the colour suffer. I also have use of a 150/f5 which without glass produces good images in the centre of the field. If I want good-to-the-edge images, I have to add a coma corrector. That adds halos around the stars, alters the colour balance, makes the stars fatter and reduces contrast.

There's no coma at f8 so I could image right to the edge of the aps-c, minus a bit for the stack alignment. Losing the cc gives more contrast and you don't get that lens 'milkiness'.

56 minutes ago, Lockie said:

I say keep glass involved

+1. Just don't allow it through!

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alacant

alacant

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1 hour ago, Lockie said:

Did you need flats?

More out of habit, I took flat frames. Although yes, Bressers have proper 2.5" r&p focusers. Maybe with the fat focuser, I won't get vignetting, but other artefacts seem to creep in if I don't include them.

You can see the focusers here...

IMG_20170719_101454.thumb.jpg.ad1c32e31bb3b0905369d1320412c0db.jpg

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Chris

Chris

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Ah I completely forgot you had the f/8, and didn't notice the 150/1200 bit to give me the clue :icon_redface: It really does give a lovely flat field at f/8 doesn't it, and I do find this at the eyepiece with my 6" f/8 Dob :) 

Coma correctors can be a pain, the best one I've had was the Baader MPCC but I know the skywatcher 0.9 did cause some issues with halos around bright stars thinking back to when I did a lot of imaging. 

I'm just wondering if it's more of a coma corrector thing than a glass telescope thing such as refractors as refractors get such high praise for imaging. I'd better be careful of starting a refractor vs reflector thing so I'll shut up now :grin:

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alacant

alacant

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10 minutes ago, Lockie said:

the best one I've had was the Baader MPCC

The only one I've found which comes close to decent stars at an affordable price is this one. Unfortunately, as soon as anyone links to it -from e.g. a forum- the price rockets:(

Yes, I'm surprised at the quality the f8 reflector gives. But likewise, I'll only mention in passing how miserable my 80mm f7 refractor was by comparison. Oh, and how it needed even more glass to make it work properly. Only joking...

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alacant

alacant

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1 minute ago, vernmid said:

no lenses have distorted the image?

Exactly that. I think it's only possible with Newtonians and maybe this type of telescope, although of the latter I know of no examples. Maybe they're called something else these days? 

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wimvb

wimvb

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3 hours ago, alacant said:

Exactly that. I think it's only possible with Newtonians and maybe this type of telescope, although of the latter I know of no examples. Maybe they're called something else these days? 

'this type' looks very much like a Ritchey-Chretien, or RC for short. But not exactly; RC have concave/convex mirrors,afaIk.

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ollypenrice

ollypenrice

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I like the image but find the glasslessness thing a bit of a distraction. What are the Bayer matrix filters made of? (Genuine question, I have no idea how they're made.) I assume you're using an OSC since you imply that there were no other filters.

The idea of an all-reflecting system is quite attractive in theory and an RC can probably get the closest to realizing this, but the original RCs used curved photographic plates because the field is not perfectly flat.

However, seen closely your stars are certainly not perfect in shape. The red outer rings are assymetrical with an orientation of assymetry varying across the frame. It isn't very distracting and I only mention it with regard to the matter of glasslessness. I wonder how it's created? Is the chip microlensed? Is it produced by the Bayer Matrix? I've no idea.

Olly

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Uranium235

Uranium235

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I think the fact that an f8 newt was used for this would explain a lot, since the coma is much reduced and hence less need for a corrector (whether the image is cropped, I dont know) - but it would be at the expense of photographic speed.

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alacant

alacant

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14 hours ago, ollypenrice said:

So what's the chip size?

aps-c is an acronym for a common size of sensor known as 'Advanced Photo System type-c'. The dimensions are about 25.1 x 16.7mm. HTH.

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ollypenrice

ollypenrice

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46 minutes ago, alacant said:

aps-c is an acronym for a common size of sensor known as 'Advanced Photo System type-c'. The dimensions are about 25.1 x 16.7mm. HTH.

Decent size, then. The scope does very well.

Olly

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