Thinking of upgrade..

[paul mc c]

Hello all, I am thinking of upgrading from my 102ed to maybe a 5" frac, it will mostly for imaging with I bit of visual. It would be a used scope with maybe £1000 tops.It will be used with a zwo 533mc Pro. 

Any advice would be greatly appreciated. Paul. 

[ollypenrice]

You need to be clear on what your objectives are or you risk landing yourself in an accidental downgrade. I take it your scope is the 102 F7, meaning it has a focal length of 714mm. This is giving you a resolution of 1.08 arcseconds per pixel with your camera. It's a near-certainty that this will be over-sampled already.  Your guide RMS would need to be no worse than half the 1.08 value, which is possible with a good EQ6 but it's probably right on the upper limit. Your sky would also have to have exceptionally good seeing to deliver real resolution at this scale. What this means is that increasing your focal length would give you no more real detail but would reduce your field of view. That could only be described as a downgrade.  Why do it?

By going up to 5" you could, in principle, go for a larger scope with a similar focal length to the present one, meaning you'd be upgrading your aperture to put more light onto each pixel. That would be fine if you could find such a telescope, but can you? And at £1000?  It's an unfortunate optical fact that colour correction becomes more difficult (read more expensive) as aperture increases, which is why even the best larger refractors have fairly slow F ratios. My TEC140 is, like your 102, F7 and it didn't cost £1000, alas. 

You already have a high resolution setup with an image scale suitable for galaxies. It's very similar to the scale at which I image galaxies. What you might find more productive in terms of giving you more choice would be a short focal length setup such as a small refractor or the remarkable Samyang 135 lens.

Olly

[michael.h.f.wilkinson]

The only scope I can think of that might have roughly the same focal length, at a bigger aperture, with excellent colour correction, coming close to that price is the Explore Scientific  MN-152 f/4.8. It does need cool-down and collimation, but if it is anything like my Meade SN-6 6" F/5 Schmidt-Newton, that is a breeze. I really love that Meade scope for wide-field views my SCT cannot manage, or for imaging smaller DSOs