Anyone using Meade DSI?

Yes Bill a truly stunning image. One of these days eh? <sigh>

Yes, just maybe in ten years i will reach that stage

@ Dave Grennan - Whats the difference between an Eq6 with built in motors ie- like the Skywatcher explorer 10", and a 'stepper' motor. Will the standard eq6 mounted explorer not do astrophotography? Why is it motorised? Just some newbie astrophoto questions.

Bear with me Stephen this might be long

Before I start let me say this. The EQ6 is a *really* great mount. Well made and definitely capable. So dont let any of this put you off. Remember you have a lifetime to upgrade the drive system if you wish.

There are many reasons why the standard eq6 drive system is not up to long exposure astrophotography.

Simply put the periodic and non periodic error (this is the deviation from a perfect tracking rate) is too great to be unguided. It is also so great that autoguiders wont work (there isnt even an autoguider port as standard). You could in theory manually guide but with such high error it is an absolute nightmare.

Primary reasons are based around the gears motors and electronics.

The gears which couple the motor shaft to the mounts worm are cheap plastic ones. They have huge backlash (play between them). The motors (DC servo motors) are not good. They dont have encoders built in to measure their performance. High quality servo systems invariably use encoders to measure how the motors are turning and feed this back to the drive system which can correct as necessary. DC servos need this because when a signal is sent to the motor to turn a bit there is an uncertainty whether it actually happens. The encoders job is to read whether the motion happened or not and tell the drive controller the result.

They also dont have enough torque to move often heavy loads which the EQ6 is well capable of carrying.

Now high quality stepper systems dont require the same feedback as servos. The electronic circuitry is simpler and much more effective. When you buy a decent stepper setup you will invariable get high quality backlash free gears attached too so theres another issue out of the way. Decent systems (servo and stepper) will have an ST4 compatible autoguider port too.

I understand the skyscan system is vastly superior to the standard eq6 drives. I didnt end up going down that road. Opting to sell the mount and buy a whole new scope instead.

Also consider this, based on my experience. Mounting large instruments such as big reflectors on any mount causes issues with wind. The whole thing acts as a big sail and makes photography impossible on all but the stillest nights. You need to consider this if photography is your primary aim. I had a 12.5inch reflector on the EQ6 for a while, but photography was out of the question for this reason. This is why my new scope is gonna be a 9.25" schmidt cassegrain.

One last thing about the eq6 I discovered. On both ends of the worms on each axis are thrust bearings. These are not the correct type and should be replaced as they allow the worm to move creating some backlash. I got a set of proper thrust bearings from Alan Buckman at AWR technology who supplied my stepper system they cost me £30 but were worth their weight in gold.

Sorry for going on so long. In short its not that you cant do astrophotography, its just that it becomes so difficult that it's impractical.

Folks - great discussion going on here with lots of food for thought!

I guess it all boils down to the old 'horses for courses' saying. From a personal viewpoint, I would say the current wave of DSLRs coming through will be giving the traditional astro CCD manufacturers serious food for thought. And the fact that DSLRs being used for astrophotography is in its (relative) infancy and therefore probably having lots of headroom for improvement can only lead to one thing - choice for us all. And as we know, choice is a good thing. It will lead to better quality and reduced prices. We all win.

Look at the stir that the new Meade RCX is causing - I can see the traditional Richey-Chretien manufacurers in the same boat - purists would point out that the RCX from Meade is not a true RC but you can't deny that consumers now have a cheaper choice in top-end optics. Purists would also argue that it could be a case of hoodwinking the consumer with serious hype, but early reports are that the RCX will give good value for money.

I guess for someone considering astrophotography its a case of weighing up the pros and cons of each imager and shortlisting those that fit their particular criteria. For some, the DSLR will win habds down for aprticular application. For others, the purpose designed CCD imager will take the biscuit. Unfortunately, there is no easy answer - and to be honest, its an extremely complex choice. I would be loathe to advise anyone to go one way or another without a detailed analysis of their requirements. And most folks are really not able to provide specifics because they are unsure of what they want to do.

Its difficult if not impossible to get a system that will do wide angle and detailed deep-sky. Trade-offs abound...

My advice to anyone wanting to get into astrophotography is to clearly state what they want to achieve from the outset then, money permitting, go for the best to avoid any kind of disappointment.

What will work for wide-field images will not work for detailed deep-sky and vice-versa. That said, you *can* spend the money and get a dual system - one mount, two OTA's (piggy-backed) and two imagers.

For the software, my point was really around buying a CCD system. If you purchase an SBIG imager, you will get purpose-designed software to control the imager and process your images. The software will focus for you, guide for you, move filter-wheels for you etc etc. For the DSLR's, I don't think the manufacturers currently supply software designed specifically geared around astrophotography. For the hardware, I guess my point was that it would be nigh-on impossible to get a DSLR to the level of a purpose-designed astro-CCD. Do DSLR's do filter wheels? Do they do cooling? Do they autoguide? Clearly no. But the user may not need any of that anyway so their choice is easier.

By the way, the DSI now has a thermo-electric cooling option - I think its less than $200. So for the price of a second-hand canon, you can get a cooled DSI-C. But then you aint gonna take a picture of Aunty Doris with the DSI (unless she's in orbit and carrying a large reflective panel :lol:)

One other point about the actual CCD's used - I'm not familiar with those used in DSLR's but it would be interesting to see the QE charts, pixel size etc. and how they match up. Don't forget that the number of pixels (6.3 million compared to a few hundred thousand) may be a misleading comparison. Other parameters are far more important - efficiency and pixel size.

As for mounts, the AP1200 will happily image in the stiffest of breezes. The wind has never caused me a problem. With a larger OTA, I suspect that there would be no difference. I think what would be more crucial in windy areas would be the support system - tripod, portable pier of fixed pier. If you use a fixed pier in a roll-off roof observatory, I''d say that any of the beefy mounts would be ok except in the strongest of winds.

To finish up, I really don;t envy anyone wanting to get into astrophotography. I have spent the last 3 years researching this and the only serious decision I have made is to buy the AP mount. I've still to decide on an OTA and imager!

Cheers
Dave McD

Don't forget that the number of pixels (6.3 million compared to a few hundred thousand) may be a misleading comparison. Other parameters are far more important - efficiency and pixel size.
Cheers
Dave McD

I quite agree with that point Dave. My S7000 has an efective 12million pixels, but no way, nor would I expect, to get astro-quality any where near as good as the Canon 300D.
Bill.