AP 130mm f/12 Superplanetary APO

[perseid]

Arief,
Any reason why you want the scope? Is it just for planetary observation? Other than planetary, I think the scope is pretty "useless".
I think any telescope over F9 will be very, very difficult to use. It is better to get a new telescope, maximum F9 focal ratio or lower and use either ED or APO lens.
In my opinion, the ideal scope would be a 10" F7 reflector. For price, for aperture and contrast!

Just my 2 cents.

Regards,
CK

at f/7, I am afraid most people will need to stand on something

It may be inconvenient for some people. But since the light path need to be deflected to the side, the finished tube would probably be around 60" or so. It'll be at eye level for an average guy (gal may have problem). The height would be quite ideal when not pointing at zenith.
You can also put it on an equatorial mount such as EQ6. Ideal for planetary imaging.

[denebman]

Arief, why not consider something like a 6 inch f/8.0 TMB? If adopting two slide tube design, the total length will only be approx. 60~70 cm, a small trolly can handle. According to TMB's statement, f/8.0~9.0 is a sweet point for an air spaced triplet apo. They just released a 130mm fluorite triplet apo, which I think is perfect on contrast and sharpness (f/9.23, ray tracing result is excellent).

[ariefm71]

hi liu ming, is the two slide tube design able to maintain perfect alignment everytime you use it or you'll need to slightly recollimate? i will definitely go with shorter fl TMB or TOA if $$ is not an issue
like everyone else in this forum, i have a soft spot for a large reflector :-)

[VinSnr]

hi liu ming, is the two slide tube design able to maintain perfect alignment everytime you use it or you'll need to slightly recollimate? i will definitely go with shorter fl TMB or TOA if $$ is not an issue
like everyone else in this forum, i have a soft spot for a large reflector :-)

what size are you looking at Bro?

[denebman]

hi liu ming, is the two slide tube design able to maintain perfect alignment everytime you use it or you'll need to slightly recollimate? i will definitely go with shorter fl TMB or TOA if $$ is not an issue
like everyone else in this forum, i have a soft spot for a large reflector :-)

In fact, the two slide tube design is not a concern when it comes to refractor. The two tubes have sufficient overlapping (with a built-in compression belt) which upon external compression automatically align the two tubes and make them concentric. At the eyepiece end, the off-axis deviation is easily controlled within star-test limit.

I think most misalignment happened on refractor is with the lens cell, especially on those with cemented design. Once the lens cell is off collimation, it is of no use spending time to improve the precision of the tube. In my opinion, what really matters is the alignment of the optical train before the focal plane, this is why people emphasize so much on the collimation of Newtonian, SCT, MCT and other compound systems, since their secondary mirrors are part of the “train” and do affect on/off axis performance. In this regard, we seldom see a telescope or an instruction that requires its user to use a precisely machined eyepiece barrel. In most cases, a loose and rattling eyepiece barrel still gives excellent results. The fact that refractors are well known for their deadly kept collimation is due to their super rigid and short lens cell, if the glass elements are confined well, they find no way to go out of collimation. In my opinion, the three so-called push-pull screws function more likely to direct the exit light cone nearest to the centre of the eyepiece rather than to serve as real collimation screws.

Besides the compactness of the dual tube design, its storing and safe carrying are also easy. You may choose to store the section with lens in a dry box and leave the rest outside. You may also hand carry this section only and send the rest as luggage during a long journey. Cleaning is also easy because both sides of the lens are accessible.

I am going to make one prototype next year.

[ariefm71]

what size are you looking at Bro?

125 to 130mm, at least f/8

Besides the compactness of the dual tube design, its storing and safe carrying are also easy. You may choose to store the section with lens in a dry box and leave the rest outside. You may also hand carry this section only and send the rest as luggage during a long journey. Cleaning is also easy because both sides of the lens are accessible.

I am going to make one prototype next year.

liu ming, you really make a very strong case here, let us know when you will start.

[rcj]

Hi arief,
Yes, like what VinSnr has mentioned the colour correction is different from the shorter f-ratio newer APs. I think someone in Spore had it before. Was housed in an observatory. NUS has an old (almost antique circa 1980) Pentax 4-inch F12. Really long, but seen Saturn once with it....it's a dear!

[ariefm71]

errr, does it mean the older AP f/12 is better-corrected than the newer f/6?

[rcj]

APF12 is almost colour free, and attractive depth of focus, especially when used on the planets and high magnification lunar/solar views. Since it has a longer focal length, one could also use correspondingly longer focal length eyepieces for extended objects like planets and yet obtain reasonable magnifications enough to discern surface features. Frankly, the F12 will be able to give you one of the finest planetary performance, more so during periods of steady seeing, where its performance will be optimized. Do note that there is a F8 reducer available for it too. Comparing it to larger SCTs, the contrast factor will be a boon, and more so in light polluted Singapore and assuming steady seeing. And yes, it is placed competitively with newer fast ratio triplets. This refractor will also be more suited to simpler (and lesser element) eyepiece designs like high quality Orthoscopics, rather than more complex 6-8 element eyepieces. And if you do get one, please let me know! Will be keen to look through it. ;P