Detection device and image forming apparatus

An image forming apparatus comprising:

• an irradiation unit that irradiates a medium with first irradiation light;
• a first optical system that comprises a first incident surface and a first refractance surface, wherein the first incident surface is substantially annular and onto which a first part of the first irradiation light is incident, wherein the first refractance surface changes the first part of the first irradiation light, which is incident from the corresponding first incident surface, into second irradiation light of which a first diameter formed when the light arrives at the medium is less than or equal to a second diameter formed when the light is incident onto the first incident surface;
• a second optical system that comprises a second incident surface and a second refractance surface that is separate from the first refractance surface and is within the first optical system, wherein the second incident surface is surrounded by the first incident surface and onto which a second part of the first irradiation light is incident, the second part of the first irradiation light is different from the first part of the first irradiation light, wherein the second refractance surface changes the second part of the first irradiation light, which is incident from the corresponding second incident surface, into third irradiation light of which a third diameter formed when the light arrives at the medium is less than a fourth diameter formed when the light is incident onto the second incident surface, a center of the first diameter and a center of the third diameter being the same point;
• a light receiving unit that is provided in a traveling direction of reflection light of the second irradiation light and the third irradiation light, which are specularly reflected by the medium, and receives the reflection light of the second irradiation light and the third irradiation light, which are specularly reflected by the medium, so as to detect a positional deviation amount of an image formed on the medium and detect a density deviation amount of the image formed on the medium;
• and
• an image forming unit that forms an image on the medium,
• wherein the image forming unit adjusts a position of the image formed on the medium on the basis of the positional deviation amount which is detected by the light receiving unit, and adjusts the density of the image formed on the medium on the basis of the density deviation amount which is detected by the light receiving unit.