18mp or 12mp canon eos?

[ollypenrice]

Oh dear im sunk then with a 18mp camera and a scope with a FL of 335mm still im happy enough with my results.

A serious question though Olly does there come a point when the pixel size value in fact covers 4 pixels in a matrix?

Alan

No, small pixels are good with short focal lengths. It's small pixels with long focal lengths that become inefficient.

I don't think I follow your second question, but are you asking if the 4 pixel matrix, seen as a whole, falls within the optimal values in terms of pixel scale? If this is your question I don't think it matters (but I'm busking here) because what matters is the signal per pixel.

Olly

[Alien 13]

No, small pixels are good with short focal lengths. It's small pixels with long focal lengths that become inefficient.

I don't think I follow your second question, but are you asking if the 4 pixel matrix, seen as a whole, falls within the optimal values in terms of pixel scale? If this is your question I don't think it matters (but I'm busking here) because what matters is the signal per pixel.

Olly

Thanks Olly and you did answer my second question.

Alan

[maxheadroom]

No, small pixels are good with short focal lengths. It's small pixels with long focal lengths that become inefficient.

I don't think I follow your second question, but are you asking if the 4 pixel matrix, seen as a whole, falls within the optimal values in terms of pixel scale? If this is your question I don't think it matters (but I'm busking here) because what matters is the signal per pixel.

Olly

Hi Olly, if I may congratulate you on your images for starters. What should I be looking at to complement a SCT with 2034mm FL? Also can you explain why long FL is bad in AP?

[Beulah]

No, just a bog standard door from my garage into a lean to shed outside so I can get access to my garden without tramping through the house. Though the whooshing sound is appealing

JD

Wow, I didn't reailse making serious modifications to the home was a symptom of being a die hard astronomer! A week ago I was only seriously thinking about getting a quote to punch a door into part of my home to enable me to move the scopes into the garden with more ease....

[jambouk]

Wow, I didn't reailse making serious modifications to the home was a symptom of being a die hard astronomer! A week ago I was only seriously thinking about getting a quote to punch a door into part of my home to enable me to move the scopes into the garden with more ease....

Any hurdles which make doing astronomy more difficult or more tedious or less enjoyable, and which can be "easily" solved, should be solved.

Jd

[frugal]

Wow, I didn't reailse making serious modifications to the home was a symptom of being a die hard astronomer! 

... this is a group of people who will happily move home in order to get a better view of the sky. Knocking a hole in the wall is the least most of these guys and gals will do

[happy-kat]

This is a brilliant site

http://www.digicamdb.com/compare/canon_eos-rebel-t3-vs-canon_eos-rebel-sl1/

[Beulah]

... this is a group of people who will happily move home in order to get a better view of the sky.

Indeed, I got very, very close to achieving that twice last year.

This is a brilliant site

http://www.digicamdb.com/compare/canon_eos-rebel-t3-vs-canon_eos-rebel-sl1/

Fantastic link. I was able to make comparisons with my faithful 500d and 550d....I see the 500d & the 1100d being mentioned more than the 500d for astro imaging.

[jambouk]

I don't need to move house, but i have a search set up on right move for an area which is still commutable to work, but which has less light pollution; it emails me daily with new properties

[mrjolly]

One thing to bear in mind with the 1100D is that I've been experiencing a problem with horrible dark streaks below bright stars. While there's lots of people with the 1100d that have no problems at all, I've been searching the net and found a few reports of other people experiencing the same problem with the 1100D so it's not an isolated case.

Bear in mind this is with stacking multiple exposures of 60s+ though!

More info here and a few links I found with other people having the issue:

http://stargazerslounge.com/topic/207337-vertical-lines-below-stars/

[ollypenrice]

Hi Olly, if I may congratulate you on your images for starters. What should I be looking at to complement a SCT with 2034mm FL? Also can you explain why long FL is bad in AP?

To answer the second question first, a long focal length isn't bad in AP. It's just challenging. A long FL makes small targets (small on the sky, that is) fill the frame. This is fine. you can get close to far away places. But it is difficult for the same reason that using ten foot long chopsticks to pick up a pea would be difficult. A small error at your end makes for a large error at the pea end! That's one way of thinking about it, at least. Using six inch long chopsticks would play to your favour but the pea in question would need to be nearer. So long focal lengths need far more accurate autoguiding and autoguiding doesn't (unless you're very lucky) just happen.

Your first question;

A long focal length instrument needs pixels large enough to give a reasonablly large number of arcsecods per pixel. The ideal number can be argued till the cows come home so shall we say that with well refined autoguiding (which won't just drop on your head the moment you fire everything up) somewhere between 1 and 2 would be reasonable.  Now were you to put my CCD camera, with its crude and enormous 9 micron pixels, into your scope you'd be imaging at 0.91 arcseconds per pixel. This is at the optimistic end of realistic. Once the pixels get smaller you are trying to resolve details which the atmosphere will probably blur out and you are pouring little light onto each pixel, so killing your signal to noise ratio.

Monochrome CCD cameras can be used 'binned 2x2' which means that four pixels can be asked to fucntion as one. If using very long focal lengths this means you can change, in effect, the size of your pixels. However, if you do this with one shot colour systems you will destroy the colour information which is collected pixel by pixel.

It's a game of soldiers but a lot of fun. Thanks for your kind comment about our pictures.

Olly

[maxheadroom]

To answer the second question first, a long focal length isn't bad in AP. It's just challenging. A long FL makes small targets (small on the sky, that is) fill the frame. This is fine. you can get close to far away places. But it is difficult for the same reason that using ten foot long chopsticks to pick up a pea would be difficult. A small error at your end makes for a large error at the pea end! That's one way of thinking about it, at least. Using six inch long chopsticks would play to your favour but the pea in question would need to be nearer. So long focal lengths need far more accurate autoguiding and autoguiding doesn't (unless you're very lucky) just happen.

Your first question;

A long focal length instrument needs pixels large enough to give a reasonablly large number of arcsecods per pixel. The ideal number can be argued till the cows come home so shall we say that with well refined autoguiding (which won't just drop on your head the moment you fire everything up) somewhere between 1 and 2 would be reasonable.  Now were you to put my CCD camera, with its crude and enormous 9 micron pixels, into your scope you'd be imaging at 0.91 arcseconds per pixel. This is at the optimistic end of realistic. Once the pixels get smaller you are trying to resolve details which the atmosphere will probably blur out and you are pouring little light onto each pixel, so killing your signal to noise ratio.

Monochrome CCD cameras can be used 'binned 2x2' which means that four pixels can be asked to fucntion as one. If using very long focal lengths this means you can change, in effect, the size of your pixels. However, if you do this with one shot colour systems you will destroy the colour information which is collected pixel by pixel.

It's a game of soldiers but a lot of fun. Thanks for your kind comment about our pictures.

Olly

Thanks Olly for this great explanation. It must be as tedious as it is repetative answering these questions time and again for clueless newbies so I speak for all of us in thanking you experienced guys for your unwavering help.

I have just struck a deal on an equatorial mount. Nothing special (CG5 GT) but it will hopefully give me a better crack than the alt az I have currently. I'm sure more questions will follow.

Best regards,

Max

[ollypenrice]

Thanks Olly for this great explanation. It must be as tedious as it is repetative answering these questions time and again for clueless newbies so I speak for all of us in thanking you experienced guys for your unwavering help.

I have just struck a deal on an equatorial mount. Nothing special (CG5 GT) but it will hopefully give me a better crack than the alt az I have currently. I'm sure more questions will follow.

Best regards,

Max

It isn't even slightly tedious. Fear not.

Olly