![[Home!]](../../images/mighty_etx.jpg){kind=small}
Last updated: 4 August 2006
|
Last updated: 4 August 2006 |
Subject: ETX Polar Home w/ DSLR Sent: Wednesday, July 19, 2006 16:55:05 From: Randy Fosler (rlsbf@comcast.net) I have an ETX-105 I want to use with my Canon Rebel XT for prime focus astrophotography. With the T-connector and camera on the back of the scope, I am limited in how much of the sky I can see in Alt/Az. I wanted to use the scope polar mounted to get a little more sky access and to take some longer exposures. However, the polar home position is with the tube pointing straight up from the base (90 degrees) -- this obviously won't work with a camera on the back. Do I perform a polar alignment without the camera and then add the camera/adapter later? The alignment will then be off somewhat when I add back the camera and counterweights. Is there any other way to do a polar alignment without starting in the normal home position? Thanks, RandyMike here: Gee, the tube points straight up in Polar Home position. Say hi to Santa Claus for me (since you live at or near the North Pole)!!! (Or did you mean "perpendicular to the base"??? Anyway, yes you can polar align without the camera attached. However, keep in mind that you may need to add some counterweight with the camera attached, otherwise you could get some slippage. In fact, if you think you mess up the alignment, just go near the target object and do a SYNC to correct the alignment for that part of the sky.
Subject: RE: Astrophotography expectations with Canon 1D Mk II and ETX-125 Sent: Thursday, July 6, 2006 01:19:36 From: Ives, Stephen (stephen.ives@citigroup.com) Thanks very much for your information. Am I correct in thinking that prime-focus photography is theoretically better than piggybacking, as you have effectively a 1200mm lens (or whatever) vs. whatever lens you have available for your camera? Does taking multiple exposures and stacking them overcome the drive inaccuracies which manifest themselves in long-exposures? One last query - do the inaccuracies of a cheaper drive which prevent long-exposure prime-focus photography (see, I'm learning all the phrases here!), manifest itself as the subject being tracked a) slowly moving out of view or b) just moving around in the eyepiece? The reason I ask is that if I took a series of images (60 exposures of 1 minute each, for example) without adjusting the scope, then with a) I will end up with some exposures with the subject only partially in the frame and the last ones with the subject completely missing. Obviously, this sequence will not be eligible for stacking. With b), the subject will just be in a slightly different position within the frame and should be stackable. This is relevant as I can use my camera either tethered to my Mac or with it's remote control/cable release to take such a sequence unattended. I found lots of moon & planetary photography done with an ETX on your website, but I couldn't find any deep-sky samples. do you have a link to any? Thanks, SteveMike here: Whether prime focus is better than piggyback depends on lots of factors and really is a matter of what the target is. But yes, prime focus is like having a 1950mm telephoto lens (with the ETX-125). Drive issues are less a problem with short exposures and stacking multiple short images to build up effectively longer images helps. Drive issues include tracking problems (too fast, too slow) causing the image to not stay precisely centered, drive smoothness causing the image to jerk around, and mounting issues causing various image problems. The higher end the telescope the better things will be. BUT you can still do astrophotography with lower end telescopes as seen in all the examples on the ETX Site. When stacking you throw out the bad images and only use good ones. Don't know why you can not find the Deep Sky examples; it is listed right on the ETX Home Page.
And:
Thanks very much for all your help. I found the Deep-Sky gallery - I'd been looking at your gallery with just the one D70 image, not the guest galleries. I think you've told me enough (and the galleries have shown) that an ETX and a t-mount would enable me to get into some astronomy and astrophotography. I just need to decide which ETX my budget will stretch to (or how much I want to pay) or I may see how much an LX90 on eBay that I'm watching gets to. Thanks again for all your advice, Regards, Steve
Subject: Astrophotography expectations with Canon 1D Mk II and ETX-125 Sent: Wednesday, July 5, 2006 06:08:01 From: Ives, Stephen (stephen.ives@citigroup.com) I am thinking of trying some astrophotography and was thinking of buying an ETX-125 to work with my Canon EOS-1D MkII. Would I be able to use this camera with this telescope (it's quite heavy) and would I be able to photograph anything other than the moon and the planets (e.g. galaxies, nebulae etc). Thanks in advance for any guidance. Regards, Steve Steve IvesMike here: Yes, you could be able to get images of some such objects but you would have to work at it. Depending on your expectations, the ETX-125 may or may not be the right telescope for you but as you can see on the ETX Site, many people do excellent astrophotography with ETX models. Weight can be a problem but you can always made a counterweight system (see the Helpful Information: Astrophotography page for lots of tips. You will need appropriate adapters to attach the camera to the ETX. You might want to start with piggyback on the ETX, then move to eyepiece projection. See the Accessory Reviews: Astrophotography page for more on adapters. You will also want a remote control device, otherwise you will be using the self-timer a lot to avoid inducing vibrations from pressing the shutter release. You will also want use the "hat trick" method of covering the lens (telescope or camera) with a dark object (I use a piece of black cardboard), opening the shutter, sliding the cover out of the way (without touching the telescope (or camera) for the duration of the exposure, covering the lens again at the end of the exposure, and then closing the shutter.
And:
I understand now (from reading your website) that piggyback mounting the camera is what's required for deep-sky photography, as the telescopes internal tracking is not accurate enough for exposure of several minutes. The piggyback mount would allow me to correct any errors in the in telescope's tracking by keeping a visible object centred in the scope manually. Also, if I am only using the telescope for guiding, then I could probably get just as good results with a cheaper ETX-90 or even an ETX-70 - is this correct? I realise that this would give me poorer results for general 'naked-eye' night-sky observing. Will I need anything other than a piggyback camera bracket e.g. an 'illuminated reticule'? I think my 1D & 300mm F4 combination will almost certainly be too heavy at about 3Kg (7lb), perhaps the 1D & 100mm F2.8 would be better. Regards, SteveMike here: Piggyback is one option that can easily be done. I've piggybacked a heavy Pentax and zoom telephoto lens on my ETX-90RA so weight is less an issue with piggyback since you have some leeway where you place the camera to retain balance. BUT at higher ISO numbers you can use shorter exposures taken through the telescope and then stack the images. Yes, tracking, even on larger telescopes, can be a problem so using shorter exposures can work out. You can see many examples of what can be done on the ETX Site. For piggyback guiding corrections an illuminated reticle eyepiece is useful but not required; you can also just use a high power eyepiece and keep the guide star centered in the eyepiece. At the image scale for piggyback photography, errors become less an issue.
Subject: Astrophotography, Oracle Observatory, and Genuine Effort Sent: Monday, January 2, 2006 16:36:08 From: John Dooley (w6zip@hotmail.com) Excellent adventure to Oracle, I keep tabs on your efforts with astrophotography and really enjoy reading about your experiences. Sorry to hear about your family cat, they are always so hard to let go of. After a pretty extensive search for an economical and portable EQ mount, I found a nice one for my Canon 20D digital SLR camera from Orion telescopes. The Mini EQ is a little equatorial mount for small telescopes and cameras plus I added the electronic drive system for another $50. It has a mini motor to regulate sidereal-rate tracking in right ascension and has additional 2X and 8X speeds + pause mode. It has an external disengage for much coarser movement of the scope (camera) by hand with the motor attached, which makes it nice for alligning your camera before tracking and exposure evolutions. I had to cut the counterweight they provided from 7.5 to about 3.75 lbs.- it was just too big for a DSLR and lens attachment. Fortunaely I have a nice bandsaw at work for this industrial task, and it came out quite nice, plus it provided me with two mini slices for mounting other, lighter weight instruments, binoculars, spotting scope, small scope for additional viewing. By adding a little white lithium greese to the worm gear, I think it smoother the slew rate somewhat also. I've attached a few shots of the unit as well as one shot of a wide field picture, north facing. Nothing spectacular at all, but again, it's part of the real challenge and reward of viewing (I think you actually said that somewhere!!)
I'm also getting ready to try out the 20D on my ETX-125 with the Scopetronix piggy back camera mount and supplied counterweights. No clear skys yet, but I'm off to Lowes to get some of that great astro-turf material to enable me to do a setup in the sandy desert just north of where I live. I'll send you a few shots when I get a chance to head out and observe. Thanks for the Mighty ETX site and keep the updates coming in regards to you astrophotography and adventures!! It's alot of fun and satisfaction.
Warm Regards for a happy and prosperous New Year, John Dooley Victorville, CA
Return to the top of this page.
Go to the 2005 Canon DSLR Astrophotography Page.
Go back to the Astrophotography Page.
Go back to my ETX Home Page.
