"Deforking" an ETX

I had a couple of emails asking how to defork an ETX telescope.

The ETX 90 and ETX 125 were optically superb scopes, but the mounts left a lot to be desired, especially the early models. I deforked my 125 a while back and it works very well on both my EQPro and ZEQ 25 mounts (although I am much more comfortable with it on the ZEQ!). My old 90 model (a 1995-vintage non-goto scope--I think Meade referred to this model as the  ETX 90 RA) worked pretty well on 3 AA batteries. Tracking was decent enough for visual work and for imaging bright, solar system objects. The other day, I dusted it off for some solar imaging and found that (most likely) the circuit board had died. I decided to defork the OTA so I could use it with the iOptron mounts.

As I've already deforked it, I can't provide pix of the process, but I can answer the question both asked: where are the screws you need to remove to release the OTA?  Here's the pic you need:

In the above image, the OTA would be vertical and the screws you need to remove fit in the four holes you can clearly see in this image. You'll need an Allen wrench (not sure what size, I just have one that fits!). After you have removed them all, simply pull the OTA forwards to remove it; it should slide out pretty easily.

I mounted my OTA on a dovetail. As the dovetail was not designed for the ETX 90 OTA, I drilled a couple of extra holes into it. The holes should align with the brass, threaded screw "sleeves" in the oblong block at the back of the OTA. 

Here's a pic:

All-in-all, it was a 10-minute job and the 90 is now usable again (see my last blog entry with the solar image).

Eclipse prep 2

Yesterday, I deforked the ETX90 OTA. I found an old dovetail and adapted it by drilling a couple of new holes in it (the existing holes were about a tenth of an inch too close together for the ETX--Murphy's Law, I guess). I mounted it on the EQ Pro and took a few images--including that below:

The Sun on June 29, 2017. AR 2664 is visible above and to the left of center

I was surprised by the image scale, compared to the ST-80--although an 80mm f/4 scope will obviously give a much bigger FOV than a 90mm f/13.8 scope. It's nice to have the 90 back in use again (I'll try some lunar and planetary images later), but the choice for eclipse scope is pretty clear: the ST-80 will provide a much better platform to image the corona.

Eclipse Prep

I plan on traveling to Nashville, TN for the solar eclipse on August 21. My plan is to take white light images with my SLRs, plus scope and solar filter. Unfortunately, the white light scope I usually use for solar work, an old 1995-vintage ETX 90, has stopped tracking. Although it worked a few weeks ago, it refuses to track now, even with fresh batteries. I think I'll probably take it off the base and add a dovetail, eventually.

The saving grace is that the filter pretty much fits my ST-80, and the 80 has a wider FOV than the ETX, which should enable some nice corona captures when I whip off the filter at totality. Today was a test of the EQPro, ST-80 and Mallincam DS16C combo, and it worked very well. The FOV is wide and the detail captured is very satisfying. Here are a couple of shots, with AR 2664 is just visible as a dot above and to the right of center in these images. I enhanced the images with an unsharp mask to bring out the "orange peel" texture. I've included an unprocessed image to show how well this combo captures this detail. The first two images, below, are processed, the last is not.

The Sun 06/25/2017 @ 20:30 UT

These images were taken with a PST-DS and Mallincam DS2.3+. Stacking and wavelet in RegiStax and final processing in Photoshop.

The Sun continues to be quiet as it moves towards what seems to be a deep minimum, but this image shows two active areas, AR2664 towards the center of the disk, and  AR2662, the lighter area at the top of the image. Neither is likely to cause flares. I've also included a couple of lightly-processed monochrome images for comparison. A small, "hedgerow" type prominence is visible close to AR2662. I've included a cropped image of it.

M51 with Mallincam DS16C and F/4 Newt

Last night blended decent seeing with a dark sky (very little light scatter). It seemed a good night to image some DSOs with the DS16C--a very sensitive, low-noise camera from Mallincam. The DS16C works very well with the Mallincam F/4 Newt and this image is the result. It's a little noisy, but not too bad for a minimally-processed short exposure stack of 10x30-seconds.