For this reason, quadruplets are primarily used only for imaging, unlike doublets or triplets.Įxplore Quadruplet & Petzval Refractor Telescopes The downside to this design, however, is that most quadruplets cannot be used visually. The quadruplet design features the field flattener built in, so you don't have to purchase an extra accessory for imaging. Nearly all doublet and triplet refractor designs will require the purchase of a field flattener or flattener/reducer combo for deep sky astrophotography. Without a field flattener, stars may appear sharp in the middle of the frame, but will appear out of focus towards the edges. A field flattener can be used to correct this - field flatteners flatten the incoming light to be parallel with the focal plane, allowing you to retain sharp, round stars even towards the edges of your image. You might be wondering: why would I need a quadruplet if a triplet already corrects for all three colors? That's a great question, and the answer has to do with another common aberration in refractors: spherical aberration. Spherical aberration is when not all light beams come to focus on the same focal plane. Quadruplet (also known as Petzval) refractors use four lens elements in their design. Overall, doublet refractors are a fantastic choice for any beginning or intermediate observer.īest for astrophotographers looking for a turnkey imaging telescope Beginners just getting started, however, shouldn't worry about chromatic aberration too much, as even a doublet can provide great views if you can look past the color fringing. This results in blue/violet-colored halos around bright objects, such as the moon, planets, and stars. Chromatic aberration is an optical imperfection where only two (red & green) of the three main colors (red, green, & blue) come to focus at the same focal plane, which we cover in more detail under the FAQ section below.
More experienced observers may notice that doublets suffer from chromatic aberration, also known as false color or color fringing. These telescopes are perfect for kids and beginners as they're intuitive to use and require very little maintenance. With that said, read on below to help you narrow down your decision even further!īest for beginners and observers on a limited budgetĭoublet refractors are the least expensive refractor design, using only two lens elements, making for an affordable entry-level telescope. Other factors, such as price, aperture, focal length, focal ratio, glass used, focuser size and design, included accessories, and whether it's an achromatic or apochromatic (APO) design should play into your decision as well. It's worth noting that the refractor optical designs of doublet, triplet, and quadruplet aren't the only aspect to consider, particularly when buying a high-end refractor, especially for imaging. Finally, those looking for an out-of-the-box solution for astrophotography may prefer the built-in field flattener (which we cover under the Quadruplet Refractor section below) in a quadruplet refractor telescope. More experienced observers and imagers may prefer the optical qualities of a triplet APO refractor telescope.
Click here to shop our wide selection of doublet refractor telescopes under $500. Requires use of a field flattener or flattener/reducer for most imaging purposesįor a beginner, a doublet refractor is more than adequate, especially if you're only planning to be visually observing. Have little to no chromatic aberration, depending on the quality of the glass used Have little to no chromatic aberration, depending on the quality of the glass used Usually have heavy chromatic aberration, unless made with good glass Some quadruplets are designed for imaging only We dive deeper into the differences between doublets, triplets, and quadruplets further below, but here's a quick overview: Doublet Refractors Each of these is a type of optical design, which is a refractor's most important trait. Doublet, triplet, and quadruplet simply refers to the number of glass lens elements inside the telescope that bring the light into focus, and each one of these types has their own pros and cons. You'll often hear terms like doublet, triplet, and quadruplet (or Petzval) used to describe refractor telescopes. No matter your skill level or your budget, the refractor design is a tried and true telescope choice for almost everyone.
Entry-level refractors are preferred for their ease of use and affordability. High-quality refractors are prized for their high contrast, aberration-free views and images. Refractors are the original telescope design, and are popular with beginners and advanced users alike. Refractor telescopes use glass lenses to bring an image into focus. In our helpful guide below, we explain the differences in layman's terms to help you decide. Refractor telescopes come in a wide range of sizes, prices, and quality levels, so it can be difficult to pick out which one is right for you.