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Posts Made By: Michael Minnhaar

June 30, 2008 03:31 AM Forum: Camping and Outdoors

Oregon Camping - Smoke?

Posted By Michael Minnhaar

I just came back from 2 days of camping (and astrophotography) near Mt Hood.
We have easterly winds - zero smoke, zero clouds until this Sunday afternoon. Saw lightning at the horizon, some 100 miles to the south, must have been soutch & west of the three sisters. But the forecast is for Thunderstorms every night this whole week all over the Cascades.

Crater Lake is great, but the Campground in the park is - astronomically - useless, deep in the woods. Go for nearby Diamond Lake, 2 Campgrounds and a rustic, but full service resort there.
Alternatively drive up for observing to the viewpoint on the south rim, near Mount Scott - a location very similar to the Bumpass Hell parking lot on Mt Lassen. Zero traffic there after nightfall.
The next destination would be Steens Mountain / Fish Lake CG at 6000ft+. Was home of the Oregon Star Party until some 10 years ago. See their website. But weather - same Thunderstorms as in the Cascades.

Michael








July 4, 2008 05:35 PM Forum: Digital SLR AstroPhotography

Live View

Posted By Michael Minnhaar

On the 40D the view on the LCD is adequate for focusing, as its up to 10x magnified.
The same view be displayed on a TV monitor at the same resolution as well as on a laptop via the USB, but I see no benefit in either for focusing.

The canon XT and XTi have no live preview of any kind. Some software can take continous exposues and display them in "quasi" real time. But when I hear a shutter fireing like this, I can't stop thinking: How long until the shutter is worn out ? They make some 10-20k actuations on those models ...

I do focus my XT by takeing 3-4 exposures with varied focus, then manually flip at full magnification through those on the display.
But this requires to have a repeatable way to set focus, I use a dial gauge for this.
I can focus this way in about 30 seconds and need no laptop at all. Compared to my 40D's live view, it's no slower or less convenient. The only benefit of the live view is, one does not need a repeatable focus mechanism.

Michael

August 13, 2008 07:26 AM Forum: AstroMart FAQ

How long does your classified ad stay up?

Posted By Michael Minnhaar

Unless its deleted, a classified stays indefinitely ... a quite usefull feature when researching an item.

Your Pentax XW ad is still there, but its 10 days old now. Your preferences are likely set to not show older ads by default. Just use the "ads from the last" pulldown menu ontop of the listing window and it will show up. Or change your display preferences in "My Accoount".

Michael

September 21, 2008 07:11 PM Forum: AstroMart FAQ

Question: disappearing classified

Posted By Michael Minnhaar

Can't find it either, seems to really be gone.Have you checked if you got an email from Herb ?

Similar deletion happend recently to me, just got a notification with a somewhat cryptic "violation of TOS" as reason. Couldn't for my life find what exactly I violated in the TOS, also asked Herb about a more particular hint, but he choose to not respond.

Michael

September 21, 2008 08:20 PM Forum: Telescope Making

Lens coating

Posted By Michael Minnhaar

L&L optical will do AR coatings. llopt dot com.

Michael

March 14, 2009 04:12 AM Forum: Eyepieces

Focuser size

Posted By Michael Minnhaar

The drawtube diameter quite often is larger than the eyepiece to avoid vignetting and/or to allow proper baffling. You will use an adaper or eyepiece holder to step this down and hold the diagonal or eyepiece.
Vixen uses 41mm ID/43 mm OD with M43x0.5 male thread for 1.25" and 58mm ID / 60mm OD with M58x0.5 female tread drawtubes for 2" eyepieces. Many focuser to day still use these sizes.

Michael

April 4, 2009 11:56 PM Forum: Digital SLR AstroPhotography

Infrared Digital Camera

Posted By Michael Minnhaar

Not for general purpose astrophotography.

It's filter passes *only* IR, not any visible light.
Another side effect of this modification is that it effectively is B&W
only, at IR wavelength all pixels have about the same sensitivity.

For astro you'd most likely want to convert it again and put
a visible light + Ha (very deep red light) filter in there.

Michael

May 16, 2009 02:22 AM Forum: Digital SLR AstroPhotography

Finding focus with a Newt

Posted By Michael Minnhaar

Under afocal imaging I uderstand imaging trough an eyepiece, effectively haveing the scope not forming a real image at all. I don't think that is what you want to do here.

You likely want do do prime focus imaging with a camera that has the image sensor fairly deep recessed into its casing, like a DSLR.
In this case you can use either move the prime focal plane with a barlow or a relay lens, but both methods have significant disadvantages and are rarely used therefore.
So there is only one way out as you have correctly identified: mechanically move the focuser towards the mirror or vice versa.

Michael


May 16, 2009 02:41 AM Forum: Telescope Making

Big aluminization job?

Posted By Michael Minnhaar

You worry about mirrors so small, they can be moved to where the chamber is ?
Here is how the next size up is dealt with:

http://subarutelescope.org/Information/Download/SMovie/flash_aluminizing.html

Michael

December 17, 2009 08:14 AM Forum: Digital SLR AstroPhotography

Has anyone used a tele-extender?

Posted By Michael Minnhaar

If you mount the extender, but without an EF lens in front of it, your
camera will show error 99 and not take any pictures at all.

The reason is that the extender has a small pin on its camera side mount
that indicates to the camera the presence of an EF lens. But when the camera
then tries to read out the lens information there is none ... the extender
itself does not qualify as an EF lens, it has zero electronics in it.

An t-mount adapter does not have that pin and thus the camera will realize
there is no EF lens and go into manual mode - thus all is fine.

Michael