andrew s

Once you are seeing limited, and not doing lucky imaging by eye or device, then all aperture brings is extra photons and possibly a bad back. Improved S/N let's you go deeper if sky brightness allows, or image with shorter exposures and/or higher cadance. It all depends on what you want to observe and how you want to do it. Spectroscopy, my thing, is photon limited so I have a 400mm ODK but it takes two people and a ramp to get it on the mount! ? You pays your money and takes your choice. Regards Andrew

I think for imaging/visual there is a definate sweat spot or small region. It is bounded by a number of factors. Less than 300mm due to the change in the effect of seeing as the " seeing cells" get resolved. S/N ratio scales as diameter not area Weight/portability goes as size^2 or size^3 depending on type Cost goes as diameter^x where x is 3 or more. This leads to the normal range of scopes we see used by SGL members. Regards Andrew

...and why he also had larger ones. Regards Andrew

Delighted you have it working. Just 4 mths from the first post, if my maths is right. You must be a relieved and happy imager. Well done all that helped. Regards Andrew

There are two main constraints, money and practicality (size and weight). In reality it depends on what you want to do and how you intend to do it. Visual v imaging , permanent obs v travel to dark sight etc. We all suffer. Find the type of observing you want to do and see what most use succesfully in that field. Regards Andrew PS then take the tablets

If you have multiple paths to earth this can cause trouble with current flowing in them v to ground. Try and collect all earth points together and connect them all to ground once. You also want to avoid earth loops where two bits of kit have an earth connection and both are grounded. This often causes hum in audio equipment. Regards Andrew

Yes I study star spectra with a home built echelle spectrograph. I have a guide head on a telescope which feeds the starlight into a fibre optic which guides the light to the spectrograph. This allows the spectrograph to be stable as it does not move as the telescope tracks the star. Regards Andrew

The reflective version should be ok with any camera. A prism adds aberrations when off axis. I use mine as the input to a spectrograph. Regards Andrew

Looking at yours it must have a reflective coating on the 45 deg face. This is mine https://www.teleskop-express.de/shop/product_info.php/info/p641_TS-Optics-Off-Axis-Guider-TSOAG9---Baulaenge-nur-9-mm.html it uses the prism with total internal reflection. You can see they are quite different. It is probably that yours uses reflection as yours is for an EOS camera with a large field. Regards Andrew

Then the 45 deg face is reflecting about 5% of the light to the guide port? It looks nothing like my teleskop services OAG prism. You live and learn. Regards Andrew

That prism looks slivered and is acting as a mirror. Is that correct? Regards Andrew

The second coloured diagram is not correct. The blue prism is the wrong way round. No known material could deviate the light at a right angle in this configuration. Regards Andrew

I think the first was correct. The light undergoes total internal reflection at the 45 deg face. The light path in the coloured diagram is impossible. Regards Andrew

Offset is to stop the AD converter from trying to convert -ve analogue values. It needs to be high enough to prevent this. It is a bit like saturation but at the low end. Regards Andrew

I thought there was an app called timber or something similar for that kind of thing? Regards Andrew

I think I have one of the smallest. A 50 micron guided fibre for solar spectroscopy. Regards Andrew

I quite agree. It was the "first thoughts" that amused me. Regards Andrew

How can first thoughts take 134 ish posts and 6 pages. It should have been built by now ? Regards Andrew

Yes, welcome to the fascinating realm that is spectroscopy. The key to the Universe ? Regards Andrew

Many a true word spoken in jest. Nice scope. Regards Andreqw

I looked at this idea some while back. For me the difficulty of collimation and focusing made me stick with a secondary mirror. It can and has been done before. Regards Andrew

All these Newts are far to pretty. This was my work horse for many years but has now passed on. Regards Andrew

If it's too tall for you wee Scots use the video camera! With the VS focused it will be very top heavy. Why not sell it and get a smaller one? Well done a magnificent effort on your part. Regards Andrew

Contacted FLO about my MBox not working 09:41 they had replied offering a replacement by 10:19 and the no cost order placed at 10:18. Oh yes and stamps to return the faulty one. Can't beat that for service. Regards Andrew

I used thin steel rod rather than coins but the principle was the same. When removed they created the gaps! Regards Andrew