IN Autumn 2008 I purchased a Meade Series 5000 127 mm refractor at the Autumn Kielder Star Camp. f/7.5, 952.5 mm focal length. 'First Light' was on 24th November 2008. I was very pleased with the result - the field of view with the CCD chip in the SBIG ST10XME camera needed no flattener - nice round stars right into the corners of the image. An accident after several years (can't remember exactly when!) damaged the fine focus mechanism, but after some head scratching and dismantling I was able to get it working again, albeit a little roughly!

As the years passed and I gradually acquired CCD cameras with larger sensors, it became evident that the field of view of my TMB105 refractor was not flat enough for successful imaging - stars towards the edges and corners were badly distorted. In July 2015 I resolved to 'do or die' and on browsing the 'net, I found a solution - a non-reducing field flattener from Teleskop Service. This one. Duly purchased direct from TS (at the time the Euro was low, so cheaper than buying in the UK!), it proved to do the job admirably.

It is necessary to space the flattener correctly as noted on the TS web page, but although TS are able to supply custom made extensions, I was able to make suitable parts on my small lathe, a useful saving!

As a bonus, the flattener also improved the images from the Meade 127 refractor. Although they were quite good without the flattener, with the larger chip of the QSI camera, there was some distortion in the corners which was nicely corrected with the TS flattener.

As I mention above, the focuser was damaged, but repaired. Nevertheless as cameras increased in weight (my QSI camera with AO unit is quite substantial) it struggled to lift and hold the camera, and the draw tube of the Crayford focuser became scored and worn with the pressure. I looked for replacements but realised that the entire focuser to tube adaptor, which included the finder bracket, would need replacing.   In Autumn 2019 I found that a 2.5" focuser from Teleskop service would nicely match the telescope, and taking the bull by the horns managed to make an adaptor. It was a scary experience - I needed to cut large diameter threads to match the tube and the new focuser, and I only had one blank aluminium disc.       Fortunately I was successful, and the telescope was transformed with the Rack and Pinion focuser easily handling the weight of the camera, and a new finder - with it standing off more than the original finder, aligning also became easier.

As it happened, the day I finished fitting the new focuser was October 26th , and that night was forecast to be clear. So first light with the new focuser was that night, and I obtained this image of Sharpless 187 in Cassiopeia. The data was collected over two nights, 5 luminance on 26th before the clouds rolled in, the remaining luminance and all the RGB on 27th - a beautiful clear night all night. QSI 8300wsg with TSFLAT2 and Starlight Xpress AO unit. Luminance 17 x 20 minutes, RGB each 5 x 20 minutes, all unbinned. North is up. Larger size

I have always been entranced by the beautiful big glass in 6 inch (150mm) refractors. And in 2022 seriously considered getting a high quality one to replace this Meade telescope and my RC10 - hopefully the unobstructed aperture and excellent contrast would allow images to match those from the RC10. But that would be marginal, and to get the preferred resolution of approximately 1 arc-second per pixel, would require unbinned imaging. Not in itself a problem - I would have nice big images, but being unbinned would take much longer to expose faint targets because CCD monochrome binning is additive. For 2x2 binning the light of four pixels is added together, so although the image size is halved, the exposures for a given brightness are much shorter. A further consideration is the reduction in clear nights due to climate change, which affects the financial decision - is it worth spending a considerable amount on an instrument which may not get a lot of use? So perhaps think again and enjoy the existing instruments. I have generally been satisfied with the performance of the 127, particularly since I replaced the focuser and used the field flattener, but it has always had a tendency to produce blue halos on most bright stars. So to look closely at the reason for the halos I experimented with a Bahtinov mask. Focus set for Luminance (IR filter) then checked the figure obtained by the individual filters. And sure enough as can be seen from this image, the Blue was slightly out of focus. (As usual click on the thumbnail.)
I did further testing using an accurate digital caliper, and found that the focuser needed to be moved out approximately 12 thousands of an inch (0.30 mm) for Blue to reach focus. To make this repeatable when imaging without going back to a bright star to refocus and then having to reposition the main target, I purchased an inexpensive (but accurate enough) digital caliper, attacked it with an angle grinder and mounted it on the focuser as shown here, using double sided sticky tape. What looks like a long dark grey spacer is in fact the field flattener, screwed to the front of the Active Optics unit with a small spacer to give the correct back focus, and also screwed direct to the focuser with an adapter to ensure that the camera is square on to the telescope. The caliper shaft had to be shortened to fit in the space between the telescope body and the AO unit. So I can accurately reposition the focuser while on target. The system works satisfactorily although of course I have to move the caliper shaft manually when the focuser moves outwards. Not a problem because I operate the focuser by hand. HOWEVER at the time of posting this (May 30th) I've been unable to see if the effect on an actual image (a bright star cluster is in mind) gets rid of most if not all the blue halos - twilight is upon me and the weather is not playing fair! If it's all in vain, well the caliper cost only £10 and it will have been an interesting experiment! Watch this space.....
Fortunately after a number of frustrating nights when it clouded over too soon, the night of 1st June played fair with 2 clear hours of Astronomical twilight, and I was able to complete the data set for my colour trials.  And here is the result - crops from unbinned images of NGC6633. Both images used the same Luminance, Red and Green image sets, the only difference being the Blue, and both combined colour sets were processed identically. QSI with SXAO, Luminance 8 x 5 minutes, RGB and B refocussed each 5 x 5 minutes, all unbinned. Pretty conclusive and definitely worth the experiment, so I'll always refocus Blue in the future. Easy with the caliper mod. There is of course still a small halo effect in the monochrome Luminance image due to the slightly unfocused blue colour, but when the corrected colour image is applied to the Luminance the halo is no longer coloured blue, so much less obvious. There is another way of doing this - dispense with the Luminance image altogether. But that would mean much longer exposures with each colour filter to get the same depth of data. Or of course spend £1000s on a better quality large refractor! The full sized image can be seen here. Although this modification worked quite well, my hankering for a larger and even better refractor eventually won, hence the sale of the 127. I would have loved a 6" refractor, but too heavy for my 'Star Party' EQ6 mount.