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Astrotrac and Canon 70-200 F4 L

ashworthacca

By ashworthacca
in Imaging - Discussion

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ashworthacca

ashworthacca

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Hi guys......my Astrotrac arrived this morning, well not just the astrotrac but the kit with Manfrotto tripod, alt/az head, ballhead etc and I have also recently acquired a Canon 70-200 F4 L lens which I propose to use solely with the Astrotrac.

Has any of you used the Canon 70-200 F4 for Astro work? Is is OK at F4 or did you find you needed to stop down a little? It comes with a lens hood.....will this combat dew or should I be looking at some other dew prevention?

What about the Astrotrac.....anyone got any tips to overcome any foibles or is it as straight forward as it at first seems.

Sorry for all the questions.:)

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brianb

brianb

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The Canon EF 70-200 F4 L lens - with or without IS - is an excellent performer and should be pretty sharp across the field at full aperture, especially when used with a APS-C sensor (it's designed to cover full frame). The lens hood is "marginally" useful, I'd certainly reccomend an active dew heater tape wrapped round it for longer exposures / unattended operation.

The Astrotrac should be fine with this lens, or even one significantly longer & heavier - I've used one (the original model) with the 300/4 and it worked great. So long as the power supply is reliable and it's mounted on a nice solid tripod (or pier) you shouldn't have any problems.

You should be able to focus the lens using AF on a bright (first magnitude) star but expect to have to refocus if the zoom control is moved. There is also a slight tendency to focus shift until the lens has cooled to ambient, but nowhere near as much as some of the lenses in the Canon range are subject to.

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ashworthacca

ashworthacca

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Damn, I have a faulty Astrotrac.:) Powers up fine but there seems to be a problem with the gears. Press the start button and it should extend an inch to stabilise the arm but the gears don't engage unless you jiggle the whole Astrotrac unit. I got it tracking thinking that it may just be a teething problem but the gears lose connection after about 10 minutes and the unit stops tracking. It also won't rewind unless you jiggle about with it to get the gears connected.

Hopefully FLO can sort me out a replacement before the clouds clear.:)

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ashworthacca

ashworthacca

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Hope you get it sorted out soon...those excellent shots by JCJC look like they've been shot at 170-200 mm (if they are not cropped) so the lens is at its "best" zoom setting.

Thanks themos:)

I'm sure It will be sorted soon but it's a little disappointing. Looking forward to giving it a run out though and if I can get anything like the shots by Jordan I'll be happy.

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ashworthacca

ashworthacca

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Power supply?

No I don't think so......checked and double checked and power to the unit was never lost.

Having to jiggle the unit to get the gears connected also convinces me that it's not power related and I did two tracking tests and it stopped in exactly the same place both times.

I could be wrong though:D

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ashworthacca

ashworthacca

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No I don't think so......checked and double checked and power to the unit was never lost.

Having to jiggle the unit to get the gears connected also convinces me that it's not power related and I did two tracking tests and it stopped in exactly the same place both times.

I could be wrong though:D

Just to expand on this.....when it stopped tracking if I pressed the arm it started tracking again. Same with the rewind, press the rewind button and it made the sounds like it was trying to rewind but the gears didn't connect....put some pressure on the arm and it connected and started to rewind.

Does that make sense?

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Wobbly Bob

Wobbly Bob

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Just to expand on this.....when it stopped tracking if I pressed the arm it started tracking again. Same with the rewind, press the rewind button and it made the sounds like it was trying to rewind but the gears didn't connect....put some pressure on the arm and it connected and started to rewind.

Does that make sense?

Thats not good Martin, lets hope FLO can sort you out.

I have the 200mm f2.8 L lens which has a dew strap attatched to it. I have a little 12v Gel battery which runs the Atrotrac and a car booster battery to run the dewstrap through a little 2 channel dew controller.

Brianb's comment about AF on a bright star is usefull as I tried to image M42 on manual focus and the 10 2min subs were all out of focus :)

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ashworthacca

ashworthacca

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Thats not good Martin, lets hope FLO can sort you out.

I have the 200mm f2.8 L lens which has a dew strap attatched to it. I have a little 12v Gel battery which runs the Atrotrac and a car booster battery to run the dewstrap through a little 2 channel dew controller.

Brianb's comment about AF on a bright star is usefull as I tried to image M42 on manual focus and the 10 2min subs were all out of focus :)

Is there any reason that I shouldn't run the Astrotrac, Canon 1000d and a dew controller unit from the same 85Ah Leisure Battery?

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davew

davew

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I can't see a problem with the power from what you've said unless the battery is duff. But then you'd know that. I've run two dew straps, the mount, guide scope, powered hub and cooled CCD camera from a leisure battery. Check the plugs first though.

I've heard of this problem before with the Astrotrac and it was fixed in no time. Who knows how much grief they get when gently loaded on and off a delivery van !

Dave.

Canon are making some fantastic L lenses these days.

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ashworthacca

ashworthacca

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I can't see a problem with the power from what you've said unless the battery is duff. But then you'd know that. I've run two dew straps, the mount, guide scope, powered hub and cooled CCD camera from a leisure battery. Check the plugs first though.

I've heard of this problem before with the Astrotrac and it was fixed in no time. Who knows how much grief they get when gently loaded on and off a delivery van !

Dave.

Canon are making some fantastic L lenses these days.

Thanks Dave.

The battery isn't duff and I'm 99% convinced it's not a power problem. Used 3 different cigarette lighter sockets and the same problem. The only thing I didn't change was the power lead that came with the Astrotrac but the power was getting to the unit all the time.

I'm waiting for Steve to call from FLO (missed his first call as I was out for lunch) so I'm sure it will get sorted.

Canon are making some superb lenses, hopefully the 17-40 F4 L will be making its way into my bag shortly.:)

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brianb

brianb

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What's the lens to have for widefield shots

Hmmm .... at the wide end, the prime lenses still outperform the zooms by a fair margin.

Some softness and illumination falloff is however common, especially when used at wide apertures. The best lenses for avoiding this are those designed for architctural work - shift lenses - which have an exceptionally large image circle, they're also very expensive.

The 17-40 f/4L actually works fairly well for what it is. Just don't expect it to be as crisp as, or illuminate the field as well as, your 70-200 f/4L.

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ashworthacca

ashworthacca

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Hmmm .... at the wide end, the prime lenses still outperform the zooms by a fair margin.

Some softness and illumination falloff is however common, especially when used at wide apertures. The best lenses for avoiding this are those designed for architctural work - shift lenses - which have an exceptionally large image circle, they're also very expensive.

The 17-40 f/4L actually works fairly well for what it is. Just don't expect it to be as crisp as, or illuminate the field as well as, your 70-200 f/4L.

Thanks Brian, food for thought.:)

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