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06-13-2008, 07:42 AM   #16
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A couple of points you need to add to the list.

The T mount adaptor for celestron telescopes can be prone to some vibration, and needs to perhaps be re-enforced with a connection from camera tripod mount to tripod in some form. This also helps with vibration. I use the bogen/monfretto long lens support on my C90

It should als be noted that the C90 focuses ny turning the front tube. the C5 as noted here, does not.

06-13-2008, 10:34 AM   #17
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Generally I find focusing with big mirrors the most difficult part of the whole picture taking process. A split screen is often of no help, as the prisms black out, when you're shooting at the fixed aperture of f/10 or slower. A good, bright matte screen works best for me, though in film days I used the specialised screen with a clear patch around a cross hair in my LX.

The main drawback of the current DSLRs for astrophotography is the mirror pre-fire. 2s or even 3s are often not enough to have the vibrations completely dampened out. It would be easy for Pentax to include a chosable pre-fire time into a C-menue, but I bet they never will do that.

As for tripods: the best are old wooden tripods, preferably from ash. I haven an oaken one, but it weights in at around 12 kgs without a head. Ash is better, dampens vibrations faster with less mass. Carbon fibre would be fine, too. But one would have to look for at least pro-video grade CF tripods to find something strong enough for the weight of a big mirror lens (my 3600mm f/15 weights in at 36 kgs... - o.k. its a telescope and mounted on a 50 kgs head)

Ben
06-13-2008, 11:04 AM   #18
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What about using the live view on the K20D and a cable release? The mirror is locked in the up position when live view is initiated. I'm not sure that it stays up thru the entire process (lotta clic 'n clack), but if it does that should solve the mirror up vibration problem (for k20d users). I agree that a firmware upgrade to include a chooseable pre-fire time in the Custom menu would solve the problem. R U listening Pentax? Let us hear you say 'I hear and I obey'.

The lens support makes a lot of sense now that i've spent a couple of hours shooting with this beast. I keep hearing money, money, money ringing in the ether! What have i gotten myself into?

Last edited by ivoire; 06-13-2008 at 11:12 AM.
06-13-2008, 11:51 AM   #19
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QuoteOriginally posted by ivoire Quote
What about using the live view on the K20D and a cable release? The mirror is locked in the up position when live view is initiated. I'm not sure that it stays up thru the entire process (lotta clic 'n clack), but if it does that should solve the mirror up vibration problem (for k20d users). I agree that a firmware upgrade to include a chooseable pre-fire time in the Custom menu would solve the problem. R U listening Pentax? Let us hear you say 'I hear and I obey'.

The lens support makes a lot of sense now that i've spent a couple of hours shooting with this beast. I keep hearing money, money, money ringing in the ether! What have i gotten myself into?
Your idea with the digital preview is great. Unfortunately a Pentax engineer thought about that possibility too - and eliminated it. The mirror goes down and up again for the real exposure... It is for exposure measuring, I think, and you can't switch it off, even not in manual mode. May be anybody else knows how to prevent that unnecessary mirror action?

And yes, supporting such a lens is the major problem, provided you get it focussed properly. As I wrote a big video tripod could work and big video heads are next to ideal for such a lens.

Ben

06-13-2008, 07:46 PM   #20
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Lowel, Haven't had any trouble with the t adapter tube on the C5. It is the same used on all larger Celestron sct (up to at least 14") and Meade sct(at least 16"). Haven't played with a C90 in 10+ years. How does the adapter tube fit to the lens? Seem to remember it going into the eyepiece hole or something. If so this is totally different than other scts. They use a semi breech lock. If the ring is tight the tube is tight. This tube is about 2" in diameter. There isn't any flex or movement, except for the camera bayonet mounts which all have slop in them. In this case screw thread would be better! Slow to change though.

ivorie, split image focus screen is more than useless at F10. It goes dark and actually hides the subject. The Olympus Varimagni finder fits Pentax dslr without ANY modification ( won't fit Olympus E dslrs). Just slip it on. gives 1.20x full field view or 2.5x center portion. If you only want full view buy the Pentax mag eyecup. It doesn't get in the way and doesn't reverse left to right images. Also looking straight thru a big lens is easier to point than using right angle.

Also shoot Olympus E300/330. Both allow setting mirror lockup time to anything up to 30sec! Love this feature. Not all tripods settle down in 3 seconds - though they should. Problem with longer delay is its harder to anticipate action, wind, etc. Also love the live view on the E330. At 7 or 10X it seems much more usable for focusing these big lenses than the Pentax K20D. Need to play with the K20D more to be sure. You ought to see the twitchiness at 25X and another 10X thrown in with live view. The atmosphere just shimmers in front of you on most days. Darn atmosphere.

A pic with C5, K20D, on medium size tripod (for me). Shoot at iso 800 about 1/500 sec. Slight levels, saturation, and sharpening. Amount I use for all my web uploads. Been watching these guys for a few weeks. Dad has been shooting Olympus E330/ 510 on Olympus 350 2.8 w/ matched 1.4 teleconverter and 2x Vivitar macro converter at the same time. It is a horse race between the two setups IQ wise.
thanks
barondla
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06-13-2008, 08:32 PM   #21
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barondla, thats a great eagle shot. I'm hoping to get a few of them soon.

I went out and shot the moon again tonite. to steady the setup i hung about 20lbs on the tripod and screwed my monopod into the camera body to steady the lens mount. it eliminated 95% of the twitch! took a little getting used to adjustments due to focus and earth rotation but the result was pretty good.

I'm guessing you mean Pentax Magnifying Eyepiece O-ME53.

Thanks to everyone for the tips and info. Its greatly reducing the learning curve.

Heres tonites shot with 2sec delay (my remote quit working) with cable release, 180th at 400iso:

Last edited by ivoire; 04-12-2009 at 10:29 AM.
06-16-2008, 07:04 PM   #22
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Thanks for the compliment ivoire. The eagle shot came out pretty well. Don't live in an area where they let you get close. That tree was out in the lake about 1000-1200 ft away. Didn't do much PP since I wanted to show what the lens could do. In full res shoot you can see the fish the eagle is eating. PP would add a little contrast, sharpen just the eagle some, and take the orangish color down a little (it was near sunset).

You certainly reduced the twitchiness. Must have a strong tripod to handle that much weight. Weight does aid stability. Being in the wind doesn't help any either.

Moon shot looks good. Shoot lots and pick the sharpest. Atmosphere can change that quickly. Astronomy people shoot hundreds of shots, pick the best. For planets they shoot web cams! Stack the best shots and actually give some observatories a run for the money. Considering trying this with the Burst mode on K20D.

Hope you get your wireless remote working again. Maybe battery died? Remote can be disassemled for battery replacement. Couldn't live without the wireless and K10/20D rear sensor. The Olympus only has wireless from front. Hard to get that to work between C5 and body. Have to hold everything just right. Oly doesn't have wired remote().

Yes, thats the right Pentax magnifier. It helps with any lens. Makes viewfinder 20% bigger. If you wear glasses it may make bottom info tougher to see. Thats better than out of focus pics.

Glad you are having fun with the big lens. Lots of work but it can be so impressive when it all clicks! Provides shots you can't get any other way. Have you tried a teleconverter yet. So far I find that the light loss is tough to deal with (even with Kenko 1.5). for wildlife may not be worth it. With K20D just crop some instead. For moon it can work with converter. You can also get a different attachment for C5 to put eyepiece in line with camera body. Holy magnification. They use this for planets.

Hope the learning curve has been shortened a little.
thanks
barondla

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06-16-2008, 07:30 PM   #23
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Barondla, had to order another remote. the battery was good, the remote just won't work at all.

haven't tried the tc yet, have a 1.5x kenko and i imagine it will make things more difficult until i get a technique down.

i have a medium weight tripod with a giotto ball head and found that adding weight and the monopod brought very good stabilization. just have to be careful not to stress the camera mount with the monopod. i'm working on devising a method of attaching it to the tube on the lens and then to the tripod leg.

hadn't thought of burst mode, will give that a try soon. tons of rain in chicago lately make me a tasty meal for the mosquitos and the clouds have not helped for shooting.

magnifier should arrive tomorrow... a plus for focus.

again thanks for the tips, they have helped immensely

06-16-2008, 07:46 PM   #24
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QuoteOriginally posted by barondla Quote
Lowel, Haven't had any trouble with the t adapter tube on the C5. It is the same used on all larger Celestron sct (up to at least 14") and Meade sct(at least 16"). Haven't played with a C90 in 10+ years. How does the adapter tube fit to the lens? Seem to remember it going into the eyepiece hole or something. If so this is totally different than other scts. They use a semi breech lock. If the ring is tight the tube is tight. This tube is about 2" in diameter. There isn't any flex or movement, except for the camera bayonet mounts which all have slop in them. In this case screw thread would be better! Slow to change though.
barondla
the assembly threads onto the outside of the eyepiece hole, but close to the armor cladding and is sometimes difficult to get tight,

As I use this both for sp[otting and photogtaphy, the adaptor is on and off frequently
06-16-2008, 08:05 PM   #25
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Hi Ivoire

That's not a mirror lens you've got there, it's more like a Howitzer by the look of it ! I reckon you've been sold a 'pup'......lol ! Incidentally, what calibre shells does it fire ?

Best regards
Richard
06-17-2008, 08:39 AM   #26
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Has anyone seen this on fleabay? *RARE* SMC PENTAX REFLEX ZOOM 400-600MM F8-12,K10D K20D - eBay (item 310059406106 end time Jun-25-08 09:38:14 PDT) Its a Pentax 400-600mm zoom. I wonder how it compares to the tokina lenses.

Last edited by Blue; 06-17-2008 at 09:10 AM.
06-17-2008, 09:17 AM   #27
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There was one recently for $750. Canadarockies mentioned it in this thread: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/27457-tokina-f...or-lens-2.html

this one is far less expensive, just not sure of the IQ and couldn't find any info on it. Starblitz 500-800mm Mirror Lens w/ 2x converter - eBay (item 330244049550 end time Jun-19-08 15:26:01 PDT)

I'm not familiar with it, but I'd like to have one. My next lba is the Tamron 70-200mm f2.8, so something like this will have to wait.

Additional tip: I received & installed the eyecup magnifier and it makes a huge difference in my ability to manual focus. I wear glasses and my manual focus ability was work. With the eyecup installed, i can see much more detail. heres a pic to illustrate the result with the Tokina 500mm f8 mirror lens:

Last edited by ivoire; 04-12-2009 at 10:29 AM.
06-24-2008, 02:07 PM   #28
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Kenko is apparently making 2 versions of an 800mm mirror lens including a Pentax mount. One with an adjustable aperture and one that doesn't.

Unfortunately, I can't read about them. Go here and click on the pics for large views of them.

ƒPƒ“ƒRー、’エ–]‰“ƒŒƒ“ƒY「ƒ~ƒ‰ー800mm F8 DX」‚ニ「ED 500mm F8 DX」
06-25-2008, 02:23 AM   #29
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QuoteOriginally posted by Blue Quote
Kenko is apparently making 2 versions of an 800mm mirror lens including a Pentax mount. One with an adjustable aperture and one that doesn't.

Unfortunately, I can't read about them. Go here and click on the pics for large views of them.

ケンコー、超望遠レンズ「ミラー800mm F8 DX」と「ED 500mm F8 DX」
This page shows the 800mm mirror lens and the 500mm conventional lens. A normal "catadioptric" mirror lens (as is the case here) can't have an adjustable aperture. There were only very few mirror lenses (pure mirrors, no catadioptrics) on the market with adjustable aperture, but they suffered from too many other shortcomings.

Ben
07-04-2008, 12:53 PM   #30
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c90 vibration issue

I posted this on another thread dealing with the C90 and vibration and thought it also applies here

https://www.pentaxforums.com/forums/283701-post9.html
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